Navigation systems for wheeled carts

ABSTRACT

Examples of systems and methods for locating movable objects such as carts (e.g., shopping carts) are disclosed. Such systems and methods can use dead reckoning techniques to estimate the current position of the movable object. Various techniques for improving accuracy of position estimates are disclosed, including compensation for various error sources involving the use of magnetometer and accelerometer, and using vibration analysis to derive wheel rotation rates. Various techniques utilize characteristics of the operating environment in conjunction with or in lieu of dead reckoning techniques, including characteristic of environment such as ground texture, availability of signals from radio frequency (RF) transmitters including precision fix sources. Navigation techniques can include navigation history and backtracking, motion direction detection for dual swivel casters, use of gyroscopes, determining cart weight, multi-level navigation, multi-level magnetic measurements, use of lighting signatures, use of multiple navigation systems, or hard/soft iron compensation for different cart configurations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/913,468, filed Mar. 6, 2018, now U.S. Pat. No. 10,232,869, entitledNAVIGATION SYSTEMS FOR WHEELED CARTS, which claims the benefit ofpriority to U.S. Provisional Patent Application No. 62/468,913, filedMar. 8, 2017, entitled NAVIGATION SYSTEMS FOR WHEELED CARTS, each ofwhich is hereby incorporated by reference herein in its entirety.

BACKGROUND Field

The disclosure generally relates to systems and methods for locatingmovable objects and more particularly to systems and methods that usedead reckoning techniques to locate movable objects such as wheeledcarts.

Description of the Related Art

A variety of methods has been used to determine the position of anobject in a tracking area. For example, a radio frequency (RF)transmitter or tag can be attached to the object, and one or morereceivers in the tracking area can monitor tag transmissions todetermine object position. However, such methods are disadvantageous ifthe tracking area is large, which requires installation of manyreceivers, or if the tracking area contains structures that attenuatethe tag transmissions. Other methods utilize a Global NavigationSatellite System (GNSS, e.g., Global Positioning System (GPS)) todetermine position. However, GNSS methods can fail if the GNSS signal isblocked or if the visibility of satellites is interrupted. Further, bothGNSS systems and RF tag and receiver systems can be expensive anddifficult to implement.

SUMMARY

Examples of systems and methods for locating movable objects such ascarts (e.g., shopping carts) are disclosed. Such systems and methods canuse dead reckoning techniques to estimate the current position of themovable object. Various techniques for improving accuracy of positionestimates are disclosed, including compensation for various errorsources involving the use of magnetometer and accelerometer, and usingvibration analysis to derive wheel rotation rates. Also disclosed arevarious techniques to utilize characteristics of the operatingenvironment in conjunction with or in lieu of dead reckoning techniques,including characteristic of environment such as ground texture,availability of signals from radio frequency (RF) transmitters includingprecision fix sources.

Navigation systems and methods can include navigation history andbacktracking, motion direction detection for dual swivel casters, use ofgyroscopes, determining cart weight (e.g., whether loaded or unloaded),multi-level navigation in a multi-level structure (e.g., buildings withmultiple floors), multi-level magnetic measurements (e.g., usingmultiple magnetometers to perform heading measurements at differentheights on the cart), use of lighting signatures to determine cartlocation (e.g., alone or in combination with dead reckoning), use ofmultiple navigation systems (for improved accuracy or in case of failureof one of the systems), or hard/soft iron compensation for differentcart configurations (e.g., a shopping cart with the child seat openversus the child seat closed).

Such systems and methods can be applied in both indoor and outdoorsettings and in, e.g., retail, transportation (e.g., airport, train,subway, bus depots), medical (e.g., hospital or clinic), or warehousesettings.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Neitherthis summary nor the following detailed descriptions purport to defineor limit the scope of the inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a retail store and associated property,illustrating components of a navigation system as a part of a cartcontainment system.

FIG. 2 illustrates a shopping cart with a navigation system and one ormore smart wheels.

FIG. 3 illustrates the components of an embodiment of a cart containmentsystem.

FIG. 4 illustrates the components of an embodiment of a smartpositioning system.

FIG. 5 is state transition diagram for an embodiment of a dead reckoningsystem working in conjunction with a smart locking wheel.

FIGS. 6A and 6B are an update loop flowchart of an embodiment of deadreckoning system with a rotation detecting smart wheel.

FIG. 7 illustrates a dead reckoning scenario.

FIG. 8 shows an example graph of acceleration versus time measured on ashopping cart.

FIG. 9 shows an example wheel rotation rate versus time measured underthe same condition as FIG. 8.

FIG. 10A shows the power spectral density versus frequency for the datashown in FIG. 9.

FIG. 10B shows a different range of the same power spectral densityversus frequency data.

FIGS. 11A and 11B show vertical acceleration versus time measured on ashopping cart rolling across a concrete surface.

FIG. 12A shows an example method for heading estimation using a deadreckoning system.

FIG. 12B shows an example method for position estimation using a deadreckoning system.

FIG. 13 illustrates a scenario of dead reckoning aided by receivedsignal strength indicator (RSSI).

FIG. 14 shows an example of a ground plan of a shopping cart containmentsystem installation.

FIGS. 15A and 15B illustrate the components of two embodiments of a deadreckoning system.

FIG. 16A shows an embodiment of a shopping cart having a smartpositioning system with a display mounted to a handle of the cart. Inthis figure, the cart has a child seat that is in a closed position(child seat up).

FIG. 16B shows the shopping cart of FIG. 16A with the child seat in anopen position (child seat down).

FIG. 17 shows a side view of an embodiment of a smart positioningsystem.

FIG. 18 illustrates a shopping cart with four castered wheels in variousdirections of motion.

FIG. 19 shows an example system of a cart navigating outdoors usinglighting signatures.

FIG. 20 shows an example system of a shopping cart navigating indoorsusing (at least in part) lighting signatures.

FIG. 21A shows an example output of a time domain three axisacceleration of an unloaded steel framed shopping cart.

FIG. 21B shows an example output of a time domain three axisacceleration of a loaded steel framed shopping cart.

FIG. 22 shows an example scenario of dead reckoning in a store in whichthe navigation system uses backtracking to improve a position estimate.

FIG. 23 shows an example of a system where multiple navigation systemssynergize.

Throughout the drawings, reference numbers may be re-used to indicatecorrespondence between referenced elements. The drawings are provided toillustrate example embodiments described herein and are not intended tolimit the scope of the disclosure.

DETAILED DESCRIPTION I. Overview

It is often desirable to track the position of an object as it movesthroughout a tracking area. A facility such as, for example, a retailstore, a hospital, an airport, or a warehouse, may wish to monitor thelocation of objects such as vehicles, carts, carriers, transports, andthe like. The facility can use object location information, for example,to track inventory movements, to improve access to and retrieval of theobjects, to identify clustering, queuing, or traffic patterns, and/or toprevent misplacement, loss, or theft of the objects. In one example, aretail store may wish to track the position of shopping carts so as toprevent the carts from being removed or stolen from a bounded area, suchas a parking lot, or to ensure that a shopping cart has passed through acheckout lane before exiting the store. In another example, a facilitymay wish to map the architectural configuration of a building by using awheeled object to measure positions of various landmarks.

It can be desirable to estimate the motion track and/or present positionof a wheeled object via dead reckoning (DR), e.g., by integratingestimated heading and longitudinal travel (e.g., distance or speed) ofthe object over time. In some cases it can be desirable to estimate thelongitudinal travel by directly counting rotations of a wheel (e.g.,with a Hall effect sensor, a rotary encoder, or an ultrasonic tuningfork, where the relevant sensors can have power efficient and/or lowlatency connections to the processing node performing the dead reckoningcalculations). In some cases it can be desirable to estimate thelongitudinal travel by other techniques. The wheeled object can be anon-motorized (e.g., human propelled) wheeled object including, but notlimited to, a cart (such as, e.g., a shopping cart, a warehouse cart, aluggage or baggage cart, an industrial or utility cart, a pharmacy orhospital cart, etc.), a wheelchair, a hospital bed, a stroller, awalker, etc.

Accordingly, various embodiments of the systems and methods describedherein provide for estimating motion of wheeled objects through deadreckoning. Some embodiments can estimate the speed of a wheeled objectby remote rotation detection or acceleration sensing, in some casescombined with analysis of a vibration spectrum of the wheeled object asit moves over a surface (e.g., a floor, a parking lot, etc.). Someembodiments can estimate speed of a wheeled object through a low-powermechanism of counting wheel rotations, e.g., an ultrasonic tuning forkin a wheel. Some embodiments can estimate current position of a wheeledobject through low-power RF techniques. Such embodiments can findparticular application to containment of shopping carts in a retailenvironment without being limited to this application.

The following describes various example embodiments and implementations.These embodiments and implementations are intended to illustrate thescope of the disclosure and not intended to be limiting.

II. Example Scenario

Example implementations of dead reckoning navigation to the shoppingcart containment problem can be found in U.S. Pat. No. 8,046,160(Navigation Systems and Methods for Wheeled Objects), which is herebyincorporated by reference herein in its entirety for all it discloses.Other examples of systems and methods for estimating motion of wheeledcarts are described in U.S. Pat. No. 9,731,744 (Estimating Motion ofWheeled Carts), which is hereby incorporated by reference herein in itsentirety for all it discloses.

For purposes of illustration, a sample scenario in which an embodimentof the navigation systems and methods disclosed herein may be used willbe presented with reference to FIG. 1. This sample scenario is intendedto facilitate understanding of one embodiment and is not intended tolimit the scope of the inventions disclosed and claimed.

In the sample scenario shown in FIG. 1, the navigation system is used aspart of a loss prevention system by a retail store 110 to reduce thetheft of shopping carts 122 from a tracking area 114. The tracking area114 may comprise, for example, a portion of a parking lot adjacent tothe store 110. An objective of the loss prevention system is to prevent,or at least reduce, the unauthorized transport of carts 122 across aboundary (or perimeter) 118 of the lot 114. In one embodiment of theloss prevention system, each cart 122 may include an anti-theft systemcomprising, for example, an alarm or a mechanism to inhibit motion ofthe cart 122. Cart motion can be inhibited by providing at least onewheel of the cart 122 with a brake mechanism configured to brake or lockthe wheel such as, for example, the brake mechanism disclosed in U.S.Pat. No. 6,945,366, issued Sep. 20, 2005, titled “ANTI-THEFT VEHICLESYSTEM,” which is hereby incorporated by reference herein in itsentirety for all it discloses. In other embodiments, cart motion can beinhibited by other wheel brakes, wheel locks, or wheel rotationinhibitors.

To prevent loss, if the cart 122 is moved across the lot boundary 118,the anti-theft system is activated (e.g., the alarm and/or the brake istriggered). In some loss prevention systems, the anti-theft system isactivated if the cart 122 detects a signal from an external transmitterpositioned near the lot boundary 118. For example, the signal may be avery low frequency (VLF) electromagnetic signal transmitted from a wireburied at the boundary 118, such as described in U.S. Pat. No.6,127,927, issued Oct. 3, 2000, titled “ANTI-THEFT VEHICLE SYSTEM,”which is hereby incorporated by reference herein in its entirety for allit discloses. Such loss prevention systems require external components(e.g., the buried wire) to be installed.

The navigation system disclosed herein may advantageously be used inconjunction with a loss prevention system, because the navigation systemautonomously enables the position of the cart 122 to be determined. Ifthe navigation system determines the position of the cart 122 to beoutside the lot boundary 118, the anti-theft system can be activated. Inone embodiment, the navigation system begins to monitor cart positionwhen the cart 122 leaves a store exit 126. The initial cart position isset to be the position of the exit, and the navigation system updatesthe position of the cart 122 as it moves throughout the lot 114. In someembodiments, the navigation system is provided with the position of thelot boundary 118, for example, as a set of coordinates. By comparing thepresent position of the cart 122 with the position of the boundary 118,the system can determine whether the cart 122 is within the lot 114. Ifthe navigation system determines the cart 122 is moving across the lotboundary 118, the navigation system can activate the cart's anti-theftsystem. In various embodiments, the navigation system can includefeatures of the anti-theft system or vice-versa. Many combinations ofthe functionality of navigation, theft prevention, wheel locking, and soforth are contemplated and various systems may choose to embody some orall of these functionalities in different combinations.

In other embodiments, the navigation system communicates the position ofthe cart 122, or other information, to a central processor or controller138, which determines whether the cart 122 has exited the lot 114 andwhether the anti-theft system should be activated. In certainembodiments, the cart 122 comprises a two-way communication system thatenables suitable information to be communicated between the cart 122 andthe central controller 138 (or other suitable transceivers). A two-waycommunication system suitable for use with the navigation system isfurther discussed in U.S. Pat. No. 8,463,540 (Two-Way CommunicationSystem for Tracking Locations and Statuses of Wheeled Vehicles), whichis hereby incorporated by reference herein for all it discloses.

Other devices and components can be advantageously used by the retailstore 110 in this sample scenario. For example, one or more markers 130a-130 c can be disposed at various locations throughout the lot 114 toserve as reference locations, landmarks, or beacons. The markers 130a-130 c can mark or otherwise indicate the position of, for example,store exits 126 (e.g., marker 130 a), the perimeter of the lot 114(e.g., markers 130 c), and/or other suitable reference locations (e.g.,marker 130 b). In various embodiments, the markers 130 a-130 ccommunicate information to the navigation system by, for example,magnetic methods or other electromagnetic methods. The navigation systemmay use information from a marker 130 a-130 c to reset the cart'sposition (e.g., to reduce accumulated dead reckoning errors), todetermine that a lot boundary 118 is nearby, or for other purposes. Insome embodiments, one or more markers (such as the markers 130 c) may bedisposed near locations of entrances/exits 142 to the parking lot 114.

In certain embodiments, the markers 130 a-130 c are configured toindicate a reference direction or other information. For example, themarker 130 a may be positioned at the exit 126 and oriented so that itsreference direction points outward, toward the lot 114. The navigationsystem can detect the reference direction and determine whether the cartis entering or exiting the store 110. Similarly, the markers 130 c canindicate an outward direction at the perimeter 118 of the lot 114. Insome embodiments, some or all of the markers 130 a-130 c can beconfigured to communicate other types of information to the navigationsystem as further described below.

In one embodiment, one or more transmitters 134 are disposed throughoutthe lot 114 and configured to transmit information to the navigationsystem in the carts 122. The transmitters 134, in an embodiment, alsoreceive information (e.g., they are transceivers). In variousembodiments, the markers 130 a-130 c (e.g., the transmitters 134 and/orthe access points 136) communicate with the carts 122 via one-way (to orfrom the cart) or two-way (to and from the cart) communicationprotocols. For example, the markers 130, transmitters 134, and/or accesspoints 136 may be configured to use electromagnetic signals tocommunicate with the cart 122. These signals may include magneticsignals and/or radio frequency (RF) or VLF signals. As used herein, RFsignals comprise electromagnetic signals having frequencies below about300 GHz, and VLF signals comprise RF signals having frequencies belowabout 20 kHz.

In other embodiments, one or more access points (AP) 136 are used tocreate two-way communication links with the carts 122. In FIG. 1, theaccess point 136 is shown positioned above the exit 126 of the store110, which beneficially allows the AP to communicate with carts 122located throughout the parking lot 114. In other implementations, morethan one AP can be used, and the AP's can be located throughout thetracking area. Access points 136 can communicate with a transceiver inthe cart 122 (e.g., an RF transceiver), which is connected to thenavigation system (and/or other components) for purposes of retrieving,exchanging, and/or generating cart status information, includinginformation indicative or reflective of cart position. The types of cartstatus information that may be retrieved and monitored include, forexample, whether an anti-theft system has been activated (e.g., whethera wheel brake is locked or unlocked); whether the cart 122 is moving andin which direction; the wheel's average speed; whether the cart 122 hasdetected a particular type of location-dependent signal such as a VLF,electronic article surveillance (EAS), RF, or magnetic signal; whetherthe cart is skidding; the cart's power level; and the number oflock/unlock cycles experienced by the cart per unit time. The accesspoints 136 can also exchange information with the navigation systemrelated to the position of the perimeter 118. In some embodiments, thecart 122 uses a received signal strength indicator (RSSI) to measure thestrength of the signal received from the access points 136 to assist indetermining the distance from the cart 122 to the access points 136 andwhether the cart is moving toward or away from the store 110. In otherembodiments, the access points 136 use an RSSI to measure the strengthof the signal received from the carts 122 to determine the location andmotion of the carts 122.

The navigation system may be used by the store 110 for purposesadditional to or different from loss prevention. In some embodiments,the retail store 110 may wish to gather information related to thepositions and paths taken by the carts 122. For example, the retailstore may wish to determine where in the lot 114 customers leave carts122 so as to improve cart retrieval operations. In other embodiments,the navigation system can communicate with other devices such as, forexample, a mechanized cart retrieval unit.

Although the sample scenario has been described with reference to a lossprevention system for shopping carts 122 in a parking lot 114 outside aretail store 110, in some embodiments, the navigation system isconfigured to determine the position of a cart 122 within the store 110.For example, the system may be used to determine whether a cart 122 haspassed through a checkout lane or whether the cart 122 has passedthrough selected aisles. In addition, the navigation system may be usedto track cart positions so as to gather information related to theclustering or queuing of carts at certain locations inside or outsidethe store 110. Many uses are possible for the navigation system, and thediscussion of the sample scenario herein is not intended to be limiting.

In some embodiments, the navigation system is disposed in or on the cart122, while in other embodiments, some of the functions of the navigationsystem are carried out by components remote from the cart 122 (e.g., thecentral controller 138). In an embodiment, the navigation system issized so as to fit within a wheel of the cart 122, a frame of the cart,or a handlebar of the cart. In certain such embodiments, the wheel is ashopping cart wheel (either a front wheel or a rear wheel). In someembodiments, the wheel has a diameter of about five inches, while inother embodiments, the diameter of the wheel is less than about fiveinches or greater than about five inches. In other embodiments, portionsof the navigation system can be disposed in one (or more) of theobject's wheels, while other portions can be disposed elsewhere in thecart 122, for example, in a wheel assembly attaching the wheel to thecart 122 (e.g., a caster or a fork), or in another location in or on thecart 122 (e.g., in the handlebars or the frame).

The navigation system can be powered by a variety of sources. Forexample, the navigation system may use electrochemical sources (e.g.,disposable or rechargeable batteries), photovoltaic power sources (e.g.,a solar cell), fuel cells, mechanical power sources, or any othersuitable source. In some embodiments, the navigation system is poweredby a generator that stores a portion of the wheel's rotational kineticenergy as electrical energy such as, for example, the wheel generatordisclosed in U.S. Pat. No. 8,820,447 (Power Generation Systems andMethods for Wheeled Objects), which is hereby incorporated by referenceherein in its entirety for all it discloses.

The power source may be integral with or remote from the navigationsystem. For example, in embodiments where the system is disposed in awheel, the power source may be disposed in the wheel and/or elsewhere inor on the cart 122 (e.g., in the wheel assembly, the handlebars, or theframe). In some embodiments, such as those facilitating a lossprevention system, the navigation system is activated only when a cart122 has exited the store 110 so as to prevent power loss while the cart122 is located within the store 110, where theft of the cart is lesslikely.

Embodiments of the navigation systems and methods may be used in otherenvironments and contexts such as, for example, a warehouse, anindustrial plant, an office building, an airport, a hospital, or otherfacility. Additionally, embodiments of the navigation system and methodsare not limited to use with shopping carts but are intended to be usedwith any other moveable objects and particularly with any other wheeledobjects. Many variations of the sample scenario discussed above arepossible without departing from the scope of the principles disclosedherein.

III. Dead Reckoning Systems

a. Basic Concepts of Dead Reckoning

A dead reckoning system can provide an estimate of the current positionof an object with information of a starting position, direction orheading as a function of time, and speed of travel or distance traveledas a function of time. This is further described in theincorporated-by-reference U.S. Pat. No. 8,046,160.

FIG. 7 illustrates a simple dead reckoning scenario map 700. An objectstarts at position 705 and travels at 45° angle (0° points north, andangle measurement increments clockwise) and at 1.4 m/s, arriving atposition 710 one second later. The object then travels at 120° angle andat 1 m/s, arriving at position 715 one second later. Finally, the objecttravels at 15° angle and at 1 m/s, arriving at position 720 1 secondlater. Dead reckoning can compute a current position (e.g. 720) from aninitial position (e.g. 705) through integration (in continuous-timedomain) or summation (in discrete-time domain) of velocity (e.g.,direction and speed) starting from the initial position.

Dead reckoning can be performed, for example, through data provided by amagnetometer and a wheel rotation counter attached to the wheeled movingobject. The magnetometer provides data on heading or direction. Therotation counter provides data through which speed can be derived. Theinstantaneous heading of a wheeled object can be obtained via a two- orthree-axis magnetometer along with the known vector components of thegeomagnetic field where the object is located. The magnetometer can bemounted to the body of the object to be tracked and function as acompass. The accelerometer can be used to adjust for the case where thesurface on which the wheeled object travels is not level.

Longitudinal speed of a wheeled object can be estimated by measuring therotation rate of one or more of the wheels. The speed can be computed asthe rotation rate (e.g., angular speed of the wheel in revolutions perunit time) multiplied by the circumference of the wheel. Multipletechniques for measuring the incremental rotation of a wheel or axis canbe used, e.g., Hall effect sensors and shaft encoders. Examples of suchtechniques are described in the incorporated-by-reference U.S. Pat. No.8,046,160.

A. Example Shopping Cart

FIG. 2 shows features of an example shopping cart 205 with featuresaccording to the present disclosure. The shopping cart 205 comprises ahandle-mounted smart positioning system 210, one or more anti-theftwheels 215 (which can brake, lock, or inhibit rotation of the wheel),and one or more optional ultrasonic vibration enhanced wheels 220. Oneor more anti-theft wheels 215 can be a smart locking wheel, e.g., awheel with a sensor, a communication system, and/or a processor inaddition to a locking mechanism. The functionalities of the navigationsystem and the anti-theft system can be distributed between the smartpositioning system 210 and the smart locking wheel 215. For example, oneor both of the smart positioning system 210 and the smart locking wheel215 can have exit/entrance event detection capability; the anti-theftfunctionality of wheel locking can be located in the smart locking wheel215 while the anti-theft functionality of user warning can be located inthe smart positioning system 210. These components are described below.FIG. 2 also shows a coordinate system 230 that can be used fornavigation calculations where the x-axis is in the forward direction ofcart motion, the y-axis is perpendicular to the x-axis and in thehorizontal direction, and the z-axis points vertically upwards.

In this disclosure, the term “user” means the individual who is using aparticular cart at a particular time. The term “customer” means theorganization, and the suitably authorized individuals therein, which canown a particular installation of the shopping cart containment system,and which can determine the policies that the particular installation ofshopping cart containment system implements. For example, the customercan be a retail store that acquires the navigation and shopping cartcontainment system, and the user can be a consumer who shops at theretail store or a store employee who retrieves shopping carts (e.g.,from a parking lot).

B. Example Smart Positioning System/Smart Locking Wheel Implementation

FIG. 3 shows a component set 300 of an example cart (e.g., a shoppingcart) tracking system. The example component set includes the followingcomponents: (1) a smart positioning system 210; (2) a smart lockingwheel 215; (3) fixed features 385 associated with exits and/or entrancesto the store; (4) system configuration and control devices 390; (5) RFbeacons or other RF features 395.

The smart positioning system 210 comprises (1) sensor elements 315 todetermine the cart's heading and speed (e.g., a magnetometer and/oraccelerometer) and, optionally, the temperature of the system (e.g., atemperature sensor); (2) an optional sensor 320 providing data fromwhich wheel rotation rate can be inferred (e.g., without the sensorbeing in proximity to the wheel), for example, a vibration sensor; (3) aprocessor and memory 325; (4) a communication system 330 to communicate(e.g., via an RF link) with a smart locking wheel 215, systemconfiguration and control devices 390, and/or RF beacons or other RFfeatures 395; (5) an optional detector 310 configured to determine thatthe cart is passing through an exit/entrance of a store (anexit/entrance event), and, in some embodiments, whether the motion isexiting the store or entering the store. In some embodiments, circuitryin a wheel performs the actual function of detection; the smartpositioning system communicates with the detection circuitry in thewheel to obtain exit/entrance information. Certain embodiments may havedetector 360 as a primary detector and detector 310 as a secondarydetector; and (6) an indicator 335 (e.g., visual and/or audible) toprovide a notification to the user to show that the cart is in a warningzone and/or about to lock. The indicator may include a displayconfigured to output text or images (e.g., a warning to the user that acontainment boundary is nearby and the wheel will lock if the wheeledobject is moved beyond the containment boundary). The indicator mayinclude a light (e.g., a light emitting diode (LED)) that illuminates orflashes as a notification to the user. The indicator may include audiblealerts or notifications. In some embodiments, the indicator comprises avoice synthesizer that can output a human-understandable message such as“cart is approaching a limit and is about to lock.” In some suchembodiments, a customer and/or a user can select the characteristics ofthe voice that is synthesized (e.g., language synthesized (e.g.,English, Spanish, German, French, Chinese, etc.), sex of the voicespeaker (male or female), age of the speaker (e.g., youth, young adult,adult, elderly)). The voice synthesizer can include one or more voicetypes for each of these characteristics (e.g., voices with differentpitches, tones, registers, timbres, etc.). The indicator may provide aselection interface (e.g., drop down menu, selection boxes, etc.) bywhich the customer and/or the user can select (or hear a sample) of adesired voice. The indicator can include a speaker to output the audiblenotification. The smart positioning system 210 may also include a lightdetector 333 for detecting ambient light signatures for use innavigation or a vertical position detector 337 (e.g., a pressure sensor)used for determining on which level of a multi-level structure the smartpositioning system is located. The functionalities of these componentsare further described below.

The smart locking wheel 215 comprises (1) a locking mechanism (e.g., abrake) 380 configured to inhibit rotation of the wheel when the lockingmechanism is actuated; (2) a wheel rotation detector 375, e.g. a tuningfork and a striker (e.g., the part which hits the tuning fork as thewheel rotates); (3) a processor and memory 370; (4) a communicationsystem 365 configured to communicate with the smart positioning system210, system configuration and control devices 390, and/or an RF beaconor other RF features 395; (5) an optional detector 360 configured todetect an exit/entrance event, and, in some embodiments, whether themotion is exiting the store or entering the store; and (6) an optionalheading/caster angle detector 383 configured to detect the heading of a(castered) wheel.

The fixed features 385 can be associated with exits and entrances to thestore. The proximity of these features can be detected by the detectorin either the smart positioning system or in the smart locking wheel.The fixed features can be used to provide an accurate reference positionto the smart positioning system (e.g., for resetting any accumulateddead reckoning position errors).

The system configuration and control devices 390 can performhousekeeping tasks such as configuration and control. The devices 390can communicate with the communication system 330 in the smartpositioning system and/or the communication system 365 in the smartlocking wheel. The system configuration and control devices 390 can bethe central processor or controller 138.

The RF beacons or other RF features 395 can transmit RF signals forentrance/exit detection and/or precision position fix.

An embodiment may be implemented with more or fewer than thefeatures/components described above. Furthermore, an embodiment may beimplemented with a different configuration than that described above,e.g., a rotation detector may be implemented in one of the smartpositioning system and the smart locking wheel, RF beacon maycommunicate with one rather than both of the communication systems 330and 365. Additionally, the functionality of the components in FIG. 3 canbe combined, rearranged, separated, or configured differently thanshown.

The smart positioning system can be disposed in one or more places inthe wheeled object. For example, some or all of the smart positioningsystem can be disposed in a cart's handle, frame, caster, wheel, etc.The smart positioning system described herein can be used forapplications other than cart containment. For example, the systems canbe used for estimating the position, path, or speed of a wheeled object.Further, in cart containment applications, the cart can include one ormore wheels configured to inhibit cart movement when activated, forexample, by including a wheel brake. For example, the wheel can lock orresist rotation when the brake is actuated. Examples of cart wheels thatcan inhibit cart movement are described in U.S. Pat. Nos. 8,046,160,8,558,698, and 8,820,447, all of which are hereby incorporated byreference herein in their entireties for all they disclose.

An example architecture 400 for a navigation system containing thesensor and processing elements used to perform dead reckoning and/orprecision fix is shown in FIG. 4. This architecture can be arepresentation of the smart positioning system 210 and the smart lockingwheel 215.

The processor/memory unit 425 provides processing and data storagefunctions for the system. The memory can comprise nonvolatile and/orvolatile memory components. For example, nonvolatile memory can be usedto store program instructions, program data, and/or state variableswhich can persist across loss of power.

The heading sensor 405 can comprise a three-axis magnetometer. Theheading sensor may additionally include a gyroscope. In someimplementations, the three-axis magnetometer functionality can beprovided by separate two-axis magnetometer (e.g., for the horizontalcomponents of the local magnetic field) and a single-axis magnetometer(e.g., for vertical component of the local magnetic field). In someimplementations, a two-axis magnetometer can be used, likely with lessprecision than an implementation with a three-axis magnetometer.

The accelerometer 410 can be of various technologies, e.g., amicroelectromechanical systems (MEMS) accelerometer, a piezoelectricaccelerometer, etc. Some implementation may use a three-axisaccelerometer; while some other implementations may use a two-axis or asingle-axis accelerometer, e.g., in cases where the wheeled object isexternally limited to level surfaces.

The vibration sensor(s) 415 can include any suitable vibration sensorsuch as the vibration sensor described in the incorporated-by-referenceU.S. Pat. No. 8,558,698, a disturbance switch, a motion switch, anacceleration switch, etc. In some embodiments, the vibration sensingfunction is performed by the accelerometer 410 and the vibrationsensor(s) 415 is not a separate component.

The rotation detection component 420 can provide data from which wheelrotation rate can be inferred. As described in connection with FIG. 3above, this component can be located in the smart positioning system 210and/or the smart locking wheel 215. In embodiments where the rotationdetection component 420 is located in the smart locking wheel (e.g., 420is mapped to 375), the processor 325 in the smart positioning system cancommunicate with the rotation detection component 375 throughcommunication systems 330 and 365 and processor 370. An example of arotation detector is a vibration sensor as stated above in descriptionof remote wheel rotation sensor 320.

In some embodiments, the rotation detection component 420 can utilizeother technologies. For example, a rotation detecting wheel may compriseelectronic/non-electronic components in its nonrotating/rotatingportion, respectively. One such embodiment can have a rotation detectingwheel comprising a Hall effect sensor in its nonrotating portion and amagnet in its rotating portion. The processor 425 can be configured tosend detection threshold and/or duty cycle as parameters to the rotationdetection Hall effect sensor 420. In some embodiments, the parametersmay comprise a valid range of speed of the wheel. The rotation detectioncomponent 420 can filter results based on this range before sendingmeasurement results to the processor 425. This may advantageously reducethe overall system power consumption. In some embodiments, the rotationdetection component 420 may not require any parameters from theprocessor 425. In some embodiments, the rotation detection component 420comprises a tuning fork and a striker.

The motion detection sensor(s) 450 can detect motion or movement of anobject to which it is attached, e.g., a wheeled object. Motion detectioncan be used to wake up the smart positioning system from a low-power(e.g., sleep) state. This can help preserve energy consumption by thesmart positioning system.

The precise position/dead reckoning reset interface 435 can receive aprecision location fix input. Such an input can be any externalstimulus, e.g., RF beacons 395, entrance/exit fixed features 385, etc.,which can be used to significantly reduce the error in the estimatedposition of the cart. After receiving a precision location fix input,the interface 435 can reset the position of the wheeled object accordingto the location in the input. This can clear any errors that mayaccumulate in position estimates through dead reckoning. Alternativelyor additionally, the precise position interface 435 can provide aposition estimate through techniques other than or in conjunction withdead reckoning, e.g., radius fix, hyperbolic fix, RSSI-aided deadreckoning, etc.

In some implementations, the locations of the reference points (e.g., incoordinates such as the coordinate system shown in FIG. 14 and discussedbelow in the section titled Example Installation and Calibration) can bepreloaded into the smart positioning system, e.g., in a siteconfiguration file. In some embodiments, reference points and smartpositioning systems are time synchronized. In some embodiments, theprecision location fix input can distinguish between on-demand and fixedreference points.

An on-demand reference point can transmit, e.g., beacon signals inresponse to a request from a smart positioning system. The smartpositioning system can transmit a location fix request to an on-demandreference point to obtain a fix, e.g., to reset accumulated errorthrough dead reckoning. The smart positioning system can be configuredto request precision location fix from an on-demand reference point onan as-needed basis. This can reduce energy consumption of the on-demandreference point and/or the smart positioning system related to precisionlocation fix and can be advantageous in installations where either orboth units are energy constrained. A reference point can be configuredto receive location fix requests only during certain time intervals. Thesmart positioning system can be configured to send a request, whenneeded, during a time interval when the reference point can receiverequests. A site configuration file can contain location, listening timeinterval, and type of power source (e.g., line-powered orbattery-powered) of reference points. The smart positioning system canincorporate such information in its determination of sending precisionlocation fix requests, e.g., having a higher/lower threshold of deadreckoning estimate error for a request to a battery-/line-poweredreference point, respectively. To reduce the likelihood of collisionsbetween or among location fix requests from more than one smartpositioning system, the smart positioning system can implement acollision avoidance/backoff protocol, e.g., pseudorandom backoff,exponential backoff.

A fixed reference point can broadcast its location periodically. A smartpositioning system can derive broadcast time from, e.g., siteconfiguration file downloaded to and stored in its memory. The smartpositioning system can activate its precision location component only atthe broadcast time. This can reduce energy consumption of receivingprecision location fix input incurred by the smart positioning system.

Examples of a precision location fix input include a radio frequency(RF) beacon at a known location and a GNSS receiver integrated with thecart (e.g. in the smart positioning system).

The user notification interface 440 can provide information, messages,and/or warnings, etc. to a user of the smart positioning system. A usernotification interface 440 can comprise audio components such as abuzzer, an audio amplifier, etc., and/or visual components such as anLED display, an LCD display, etc.

The configuration/status interface 445 can provide configuration and/orstatus information to service and/or maintenance personnel. In someembodiments, the configuration/status interface 445 can share hardwarecomponents with the user notification interface 440. In someembodiments, the configuration/status interface 445 may be implementedremotely, e.g., on a system configuration and control device 390.

The power supply 430 supplies electrical power to the smart positioningsystem. The power supply 430 can comprise, e.g., one or more batteries.

Functions shown as separate in the example architecture do notnecessarily correspond to separate hardware components in animplementation; for example, the vibration sensing 415 and motiondetection 450 functions may be performed by a single hardware component,or either function may be performed by the accelerometer 410.

C. Example Dead Reckoning System/Locking Smart Wheel Operation

FIG. 5 shows a state diagram 500 of dead reckoning system logic and astate diagram 560 of smart locking wheel logic in an embodiment of ashopping cart containment system. A dead reckoning system can be anembodiment of a smart positioning system which uses dead reckoning asthe primary technique for position estimation. In FIG. 5, arrows withdashed lines denote transitions initiated by the other unit (e.g., astate transition in the dead reckoning system initiated by the smartlocking wheel, or vice versa). Arrows with solid lines denotetransitions initiated within the respective unit itself.

For the purpose of illustration, the state transition diagrams 500 and560 do not cover indoor navigation: the dead reckoning navigationprocess starts when the cart exits the store and stops when the cartreenters the store. An embodiment according to the present disclosurecan have indoor navigation mode (for example, see section below titledIndoor Modes). Such an embodiment can have different state transitiondiagrams.

The state diagram 500 for a dead reckoning system begins at state 505,wherein a shopping cart is indoor with the dead reckoning system in aninactive mode. State 505 is selected as the initial state for thepurpose of illustration, not by way of limitation. An implementation ofa dead reckoning system may work its way through the state diagram fromanother operating state. A sensor for exit/entry/limit line detectionsuch as 310 can monitor the presence of an exit marker. Until the sensordetects an exit marker, the dead reckoning system can remain in state505. After the sensor detects an exit marker, the dead reckoning systemcan transition to state 510.

Exit markers can be located at or near an exit from the building (e.g.in the door frame, in the threshold of the door, etc.). Exit markers canuse 2.4 GHz transmitters, magnetic barcodes, EAS, etc. Transmission froman exit marker may sometimes be received farther inside the building(e.g., a store) than desirable for detecting an exit event because thetransmitter power of the exit marker may need to be high enough thatshopping carts can consistently and reliably detect exit events. Such ahigh level of power can result in an exit detector 310 and/or 360sometimes detecting an exit marker while the cart is still inside thestore (e.g., a customer picking up merchandise that is along the frontedge of the store). In state 510, the navigation system can analyze orlearn the marker's RSSI over time to reduce the likelihood of falsepositive detections. For example, an embodiment can correlate anincreasing level of RSSI followed by a decreasing level of RSSI (withthe intervening peak likely indicating a close distance from an exitmarker) with a concurrent change in vibration signatures (e.g., fromvibrations on smooth indoor flooring to vibrations on concrete,indicating an exit event). A positive correlation can increase theconfidence level of a true positive detection of an exit event. If noRSSI peak is found, the logic transitions back to state 505. If an RSSIpeak is found, the logic transitions to state 515.

The logic may also enter state 515, directly from state 505, via twomechanisms. First, a precision exit detection by the dead reckoningsystem can cause the logic to transition directly from state 505 tostate 515 (denoted by the solid line). As described herein, a deadreckoning system can include a feature such as beacon detection whichcan be used to detect an exit event. Secondly, a wake-up signal from thesmart wheel can cause the logic to transition directly from state 505 tostate 515 (denoted by the dashed line). An installation of a carttracking system within a single store may use one or a plurality oftechnologies for entrance/exit markers, e.g., 2.4 GHz transmitters, 8kHz transmitters, magnetic barcodes, EAS, etc. Thus, an exit/entranceevent may be detected by either the smart wheel or the dead reckoningsystem, which can inform its counterpart of the detected event.

At state 515, the dead reckoning system starts dead reckoning navigationmode. The system can synchronize its state with the smart wheel andtransition to state 520. In an embodiment, the smart wheel and deadreckoning system can have periodic, two-way communications forhousekeeping purposes when the cart is not in the dead reckoningnavigation mode. The period of such communications can result from atrade-off between latency and power consumption and can be, for example,1 to 2 seconds, e.g., 1.8 seconds. When the cart is in the deadreckoning navigation mode, the period of such communications may bedecreased, e.g., to less than 1 second. When the cart is in or near awarning zone and/or the containment boundary, the period may bedecreased, e.g., to its lowest operational value such as less than 0.75or 0.5 second (or some other value). Outside the business hours of thestore, or if the cart has not been active for a long time (e.g., 30minutes, an hour, etc.), the period may be increased, e.g., to minutesor tens of minutes. At the start of the dead reckoning navigation mode,there can be a burst of communications between the smart wheel and thedead reckoning system for the purpose of navigation. The burst ofcommunications can synchronize the states of the two units.

At state 520, the system can receive rotation data from the smart wheelin a steady state of dead reckoning functionality. The system canperform speed estimation directly from wheel rotation data and/oracceleration data if such data is available and reliable (state 520).Additionally or alternatively, the system can perform wheel rotationrate or speed estimation through data analysis (e.g., spectral analysisand/or acceleration data analysis) if wheel rotation data is notavailable or is unreliable (state 540). Spectral analysis is describedbelow.

If an entrance event (e.g., the cart is moved into the store through anentrance) is detected by either the dead reckoning system or by thesmart wheel, the logic can transition from state 520 back to state 505.If the cart is detected to have entered a warning zone, the logic cantransition to state 525. The system can announce warning, e.g., throughaudio and/or visual outputs from user warning component 335. If the cartis detected to have exited the warning zone toward the store, the logiccan terminate the warning and transition back to state 520. On the otherhand, if the cart is detected to have exceeded the containment boundary,the logic can transition to state 530. At state 530, the dead reckoningsystem can initiate a locking sequence of the smart wheel. When thesmart wheel communicates to the system that the locking sequence iscompleted, the logic can transition to state 535.

When the cart is moved back into the store from the parking lot, anentrance event sometimes may not detected, and the system does nottransition back to state 505 (DR inactive). This may be due to errorconditions that cause the cart to miss detecting a door marker. Forexample, the exit/entry/limit line detector 310, 360 may not detect amarker at a store entrance/exit. In such a situation, the dead reckoningsystem may continue to be active while the cart is inside the store.This may be disadvantageous, because the smart positioning system willcontinue to process dead reckoning navigation data, which consumesbattery power and shortens the time to when the battery needs to berecharged or replaced. Further, the cart may make multiple trips aroundthe store (before exiting out to the parking lot), and accumulatednavigation error inside the store may cause the smart positioning systemto incorrectly infer that the cart is near a lock perimeter. This maycause a spurious transition to states 530, 535 in which the smart wheellocks inside the store, which may inconvenience the shopper or storestaff.

To reduce the likelihood of inadvertent in-store operation, the storecan include one or more RF beacons 395 disposed in the store. Forexample, FIG. 14 (further described below) shows an RF beacon 1411disposed in store interior 1410 (e.g., toward the center of the store).The signal strength or the directional antenna pattern of the RF beacon1411 can be set such that the RF output of the beacon has a level thatis perceivable by the communication systems 330, 365 of the smartpositioning system 210 or the smart locking wheel 215 substantially onlywithin the store interior 1410 and not outside the store (e.g., in anadjacent store or the parking lot). If the signal from the RF beacon1411 is detected by the smart positioning system, the system logic canassume that the cart is actually inside the store (because the RF signaldoes not extend beyond the store boundaries), and the system statetransitions from state 520 (steady state DR) to state 505 (DR systeminactive), even though an entrance event was not detected. The RF beacon1411 thereby acts somewhat like a kill-switch to shut off dead reckoningwithin the store. Because the RF signal strength or antenna pattern ofthe beacon can be adjusted not to extend beyond the store boundaries,this kill-switch behavior of the beacon 1411 will not inadvertently shutoff dead reckoning outside the store (e.g., in the parking lot). In thelocked state 535, if the system detects that the cart has moved back towithin the containment boundary, e.g., by being dragged backwards, thelogic may transition to state 545. The logic may also transition fromstate 535 to 545 after receiving a retrieval command. A retrievalcommand can come from a handheld unit (e.g. in the hand of a storeemployee) such as a CartKey remote control, or from a CartManagerpowered retrieval unit, both available from Gatekeeper Systems (Irvine,Calif.). Either way, the retrieval signal can unlock the wheel and cankeep the wheel unlocked for a certain period of time (e.g., severalseconds to a few minutes) after the retrieval signal stops even if thecart may still be outside the containment boundary. The cart cancontinue to perform dead reckoning navigation while it is beingretrieved.

At state 545, the system can initiate an unlocking sequence of the smartwheel. When the smart wheel communicates to the system that theunlocking sequence is completed, the logic can transition to state 520.

The state diagram 560 may be applied to a smart locking wheel 215. For acart with a plurality of smart locking wheels, one can be selected asthe master wheel. The state diagram 560 may then be applied to themaster wheel. The state diagram 560 begins at state 565, wherein ashopping cart is in an indoor inactive mode. Similar to what is statedabove for state diagram 500, state 565 is selected as the initial statefor the purpose of illustration, not by way of limitation.

At state 565, a sensor for exit/entry/limit line detection such as 360can monitor the presence of an exit marker. Until the sensor detects anexit marker, the smart locking wheel can remain in state 565. After thesensor detects an exit marker, the smart locking wheel can transition tostate 570.

The description above of state 510 can be applicable to state 570,including the causes of transitions into and out of the state. Anembodiment may have a sensor for exit/entry/limit line detection in thedead reckoning system, the smart locking wheel, or both. Depending onthe system configuration, e.g., the number and/or location of suchsensors, states 510 or state 570 may be omitted from the respectivediagrams.

The logic may enter state 575 directly from state 565 via precision exitdetection by the smart wheel. As described above in connection with FIG.3, a smart wheel can include a feature such as beacon detection whichcan be used to detect an exit event. An embodiment can have such afeature in the smart wheel and/or the dead reckoning system. Dependingon the system configuration, e.g., the number and/or location of suchfeatures, the direct transition from state 565 to state 575 or thedirect transition from state 505 to state 515 (the solid line) may beomitted from the respective diagrams. At state 575, the smart wheel caninitiate rotation counting functionality. For a smart wheel capable ofdetecting an entrance event (e.g., a smart wheel with sensor 360), upondetecting an entrance event, the logic can transition back to state 565from state 575. Without detecting an entrance event, or upon asynchronization request from the dead reckoning system (e.g., during thetransition from state 515 to state 520), the smart wheel can synchronizeits state with the dead reckoning system and transition to state 580.

A smart wheel may also enter state 580 directly from state 565 uponreceiving a command from the dead reckoning system to begin countingrotations. An embodiment of the system can perform synchronizationbetween the dead reckoning system and the smart wheel in connection withthis command, such that at the beginning of state 580 the two units aresynchronized. The smart wheel may exit state 580 back to state 565 uponreceiving a command from the dead reckoning system to stop countingrotations.

Upon receiving a lock command from the dead reckoning system, the smartwheel can transition to state 585, wherein the locking mechanism of thesmart wheel is engaged. Upon receiving an unlock command or a retrievalcommand from the dead reckoning system, the smart wheel can transitionback to state 580 from state 585.

As described above, in some circumstances a smart locking wheel may missdetection of an entrance marker when the cart enters a store. To preventdead reckoning inside the store (which, e.g., may reduce battery life orlead to inadvertent wheel locking), the communication system 365 of thewheel can detect an RF signal from the RF beacon 1411, and the wheel cantransition to state 565 (indoor inactive) while inside the store.

D. Example Dead Reckoning System Processing

FIGS. 6A and 6B shows an example of the basic update loop underconditions where rotation is being reliably detected in the wheel. Theblocks on the left side comprise processes in a dead reckoning system;the blocks on the right side comprise processes in a rotation detectingsmart wheel.

For purposes of illustration and not for limitation, the loop starts atblock 604. At block 604, the dead reckoning system and/or the smartwheel detects an exit event. At block 608, the dead reckoning system candetermine a minimum possible distance and/or time to emitting a warning.At block 612, the dead reckoning system can send wheel rotation countsand/or timeout parameters to the smart wheel. The timeout parameters maybe determined based, at least in part, on the minimum possible distanceand/or time as determined in block 608. For example, if the minimumpossible distance is small, the timeout period can be short, and viceversa. A choice for a timeout period can be a period which under worstcase conditions and/or assumptions is still too short for the cart tocross the nearest containment boundary.

At block 616, the dead reckoning system can accumulate magnetic,acceleration, and/or vibration data. Time series may be formed fromaccumulated data, as represented in block 620. The time series can beprocessed through signal processing techniques to derive usefulinformation. For example, acceleration data can be used to estimate thefrequency of wheel rotations, as described below in the section titledLongitudinal Speed Estimation via Vibration Analysis.

At block 624, the dead reckoning system determines whether entry orreentry into the store is detected. If yes, the flow returns to block604 and repeats therefrom. If no, the flow proceeds to block 628. Atblock 628, the dead reckoning system determines whether a precisionposition fix has been received through, e.g., precise position interface435 in FIG. 4. If yes, the process proceeds to block 644. Otherwise theprocess proceeds to block 632.

At block 632, the dead reckoning system determines whether one or moresignatures of the magnetic, acceleration, and or vibration data areanomalous. If yes, the dead reckoning system can proceed to performspecial processing based on the specific anomaly detected, as shown inblock 636. After special processing is completed, the flow may continuefrom a suitable block, e.g., block 640 if wheel rotation data is used inprocessing, block 644 if wheel rotation data is not used. If no, theprocess proceeds to block 640, in which the dead reckoning system candetermine whether rotation data has been received from the smart wheelsince the last iteration. If no, the process returns to block 616.Otherwise the process proceeds to block 644.

An anomalous magnetometer signature may, as an example, be produced whenthe magnetometer is in the vicinity of a vehicle, e.g., a large sportsutility vehicle. The vehicle may distort the magnetometer reading suchthat vector magnitude of the reading deviates significantly from theexpected geomagnetic field for the location. This deviation can producean anomalous signature in the magnetometer data.

As another example, an anomalous signature may be produced by casterchatter (e.g., a castered wheel swinging rapidly back and forth).Normally, the wheel magnetometer may output a nominal caster anglerelative to local magnetic north of arctangent 2 (Y axis magnetic field,X axis magnetic field), where the coordinate axes match those of thecart. The smart positioning system magnetometer, after the headingestimation processing described below in FIG. 12A, can provide thecart's heading relative to local magnetic north. An embodiment canprocess both the caster axis measurements and the cart heading through abandpass filter with passband, e.g., 0.5 Hz to 25 Hz, 0.1 Hz to 50 Hz.When the phenomenon of caster chatter is present, the filtered casteraxis residual sum of squares (RSS) value can be both greater than threeto seven (e.g., five) degrees per second and greater than 2.5 to 3.5(e.g., 3) times the cart heading rate of change over the same period.

Special processing for caster chatter can comprise: 1) ignoring rotationdata from the wheel for the purposes of dead reckoning; 2) usingspectral analysis to estimate wheel rotation rate; 3) optionallyapplying a notch filter to the cart X-axis vibration data, where thecenter notch frequency can be located at or near the center frequency ofthe caster oscillation.

A third example of anomaly can occur when a rotation-indicating wheelhas poor contact with the ground, e.g., the wheel rotates at a fairlyconstant speed and stops rotating quickly due to friction in thebearings. Under this condition, the acceleration in the cart's Xcoordinate as measured by a low pass filtered accelerometer output maybe less than the acceleration implied by the rotation count by asignificant ratio, e.g., less than half, two-thirds, etc.; An embodimentmay impose an additional requirement for the condition that theintervals between successive rotation detections over a period of atleast two rotations indicate an acceleration or deceleration in excessof 1 m/sec² (=0.1 gee). As an example, if the cart's X-axis acceleration(e.g., as measured by the accelerometers in the smart positioning systemrotated to the cart reference frame) when low pass filtered at, e.g., 3to 5 Hz indicates a much smaller number than 1 m/sec², e.g., less than0.5 m/sec², it can be inferred as a signature of anomaly of poor wheelcontact with the ground. Additionally, an embodiment may compare thesign of acceleration (e.g., negative means deceleration) reported by theaccelerometer versus the wheel. If the signs are the opposite, theembodiment can infer poor wheel-ground contact.

Special processing consists for poor wheel contact with the ground caninclude: 1) ignoring rotation data from the wheel for the purposes ofdead reckoning; 2) using spectral analysis to estimate wheel rotationrate; 3) monitoring the rotation data to determine if or when goodground contact has resumed. For example, the wheelacceleration/deceleration implied by the rotation intervals has beeneither: a) of the same sign and within a factor of two in magnitude ofthe low pass-filtered cart X-axis acceleration as described above; or b)less than 0.3 to 0.7 (e.g., 0.5) m/sec² in magnitude for some programmedinterval (e.g. five to ten seconds).

At block 644 the dead reckoning system can update estimated position,speed, and/or other state variables. If the process enters block 644directly from block 628, the position update can comprise resetting theestimates of position and other state variables based, at least in part,on data from the precise position fix. If the process enters block 644from block 640 or 636, the update to estimates of position and otherstate variables can comprise estimates based, entirely or partially, ondead reckoning.

At block 648, the dead reckoning system determines whether the cart iswithin a warning distance from a cart containment boundary, e.g., withina warning zone. If no, the process returns to block 608. If yes, thedead reckoning system can proceed to block 652, where in the system caninitiate a lock and/or warning sequence, e.g., as illustrated in state525 through 535 in FIG. 5.

As shown on the right of FIG. 6A, at block 664, the rotation detectingsmart wheel can wait for rotation counts and/or timeout parameters fromthe dead reckoning system (sent at block 612). At block 668, the smartwheel can accumulate time stamped rotation and/or validity indicators. Avalidity indicator indicates whether the rotation counts are valid,e.g., if measured data shows poor wheel-ground contact, the validityindicator indicates an invalid count, e.g. via a low state. Time seriesmay be formed from accumulated rotation data, as represented in block672.

At block 676, the smart wheel determines whether a lock field is set(e.g., to 1). A lock field can be set in the smart locking wheel whenthe cart has exceeded the containment boundary. FIG. 6 describes anembodiment in which the smart wheel can determine if conditions forlocking the cart are satisfied. FIG. 5 describes an alternativeembodiment in which the dead reckoning system can make such adetermination. If yes, the smart wheel can communicate with the deadreckoning system, which can in turn initiate a lock sequence at block652. Otherwise, the smart wheel processing can proceed to block 680.

At block 680, the smart wheel can determine whether the accumulatedtimestamp rotation and/or validity indicators show evidence of chatter,skip, etc. If yes, the smart wheel can communicate with the deadreckoning system, which can in turn perform detection of anomaloussignature detection at block 632. If no, the smart wheel processing canproceed to block 684, in which the smart wheel can determine whether arotation count limit or timeout has been reached. This can help reducethe frequency of communication from the smart wheel to the deadreckoning system, thereby possibly reducing energy consumption. If arotation count limit or timeout has been reached, the smart wheel canpreprocess rotation data and send the preprocessed data to the deadreckoning system. The preprocessing may reduce the amount of datatransmitted to the dead reckoning system, thereby possibly reducingenergy consumption. For example, preprocessing can comprise datacompression to reduce the energy cost of, e.g., the radio transmissionif RF communication is used. If a rotation count limit or timeout hasnot been reached, the processing can return to block 668 where dataaccumulation continues.

In some embodiments, the wheel accumulates timestamped rotation data inits local memory. Optional additional data such as magnetometer valuesand/or accelerometer values may be captured as well, to be used forassessing the reliability of the rotation values (e.g., for determiningwhether the caster is chattering).

As described above in connection with block 684, after either somenumber of rotations has been detected, or a given amount of time haselapsed, the smart wheel can send the accumulated data to the deadreckoning system. For example, the wheel may be electrically connectedto the dead reckoning system or may communicate with the dead reckoningsystem using wired or wireless techniques.

While the wheel is accumulating the rotation data, the dead reckoningsystem accumulates raw magnetometer, accelerometer, and vibration data.An embodiment can be configured to collect only a subset of these typesof data, or to collect another type of data, e.g., gyroscope data. Somecombinations of data types can advantageously improve the accuracy ofdead reckoning estimates. For example, as described below in sectiontitled Steady State Speed Estimate Update Loop, rotation data can beused to derive accelerometer offsets. As another example, wheel rotationdata from both a front castered wheel and a rear axle wheel can be usedin conjunction with magnetometer data in heading estimates.

In some embodiments, in steady state dead reckoning navigation, thewheel accumulates rotation timestamps (e.g., a time offset from somereference time to the detection of the Nth rotation of the wheel, whereN is an integer); the dead reckoning system accumulates the data whichcan be processed to produce attitude and heading information (e.g.,magnetometer and accelerometer data).

IV. Dead Reckoning Methods

Some shopping cart containment embodiments can have constraints whichmay make otherwise practical solutions challenging or impractical toimplement. Some of these constraints can also apply in other contexts orapplications. These constraints include: heading estimate accuracies ofwheel; asymmetric energy constraints between the dead reckoning systemversus the smart wheel; a lack of a viable connection between a rotationsensor and a dead reckoning system. It is advantageous to minimize theeffects caused by these constraints.

a. Reducing Error in Heading Estimation

Several factors may make it difficult to obtain an accurate heading froma magnetic sensor placed inside a shopping cart wheel, e.g., castereffects, 50/60 Hz coupling, and/or buried ferromagnetic objects.

A typical front wheel of a shopping cart is castered about the verticalaxis. If the caster is bent from vertical, then the wheel can oftenrapidly oscillate about the caster axis, e.g., with a frequency on theorder of 0.5 Hz to less than 10 Hz. The oscillation can bequasi-periodic, but not exactly so. If a low pass filter is used to dampthe caster oscillation effect on the heading estimate, the cutofffrequency of the low pass filter would be less than 0.5 Hz, much lowerthan the cutoff frequency of a few Hz as described in U.S. Pat. No.8,046,160. Thus, the responsiveness of the magnetometer plus thelow-pass filter to actual changes in the cart heading may be too slowfor accurate dead reckoning.

Large currents at power line frequency or its harmonics (such as thesecond harmonic driven by fluorescent lighting, multipole harmonics fromelectric motors starting up) on buried power lines can producesubstantial magnetic fields at the wheel. While these can largely befiltered out with bandstop filters, the induced fields at the cart canbe strong enough to induce significant nonlinearities in a cart-mounted,low-power magnetometer. In some implementations, these nonlinearitiescan be challenging to filter out and can cause inaccuracies in headingestimates.

Large ferromagnetic objects such as structural steel or iron pipes canproduce a substantial soft iron distortion up to several centimetersabove the surface. The induced fields at the wheel can be strong enoughto induce significant nonlinearities in a wheel-mounted magnetometer.

The accuracy of the heading estimate can be improved using one or moreof the following techniques: (1) For an embodiment including athree-axis magnetometer rigidly mounted to the body of the wheeledobject and a three-axis accelerometer mounted in a fixed anglerelationship to the magnetometer, the magnetometer can be compensatedfor tilt. Tilt of the ground surface can affect the accuracy of themagnetometer. A higher grade of slope for tilt results in a greaterprojection of the vertical component of the geomagnetic field onto thereference horizontal frame of the cart, which is parallel to the(sloped) ground. This can cause greater inaccuracies in the magnetometeroutput. (2) Performing hard and soft iron calibration of themagnetometer as mounted to the body of the wheeled object. This is thesubject matter of U.S. Pat. Pub. No. 2017/0067981, titled “Magnetometerand Accelerometer Calibration for Cart Navigation System,” which ishereby incorporated by reference herein in its entirety. (3) Applyingdigital filter algorithms to the raw magnetometer output to reducenoise, in particular removing the local power line frequency (e.g., 50or 60 Hz, depending on geographic location) and its harmonics. (4)Combining the magnetometer output with a gyroscope output (e.g., a MEMSgyroscope) via a filter such as a Kalman filter. A gyroscope can provideheading information which can be used in conjunction with or in place ofmagnetometer data. A gyroscope may provide better response time to quickheading changes and/or tight turning radius than a magnetometer or anaccelerometer because a gyroscope can output turn rate directly. Thebetter response time can result in more accurate dead reckoningtracking. A gyroscope can provide data to corroborate outputs from othersensors. For example, inconsistent data from the magnetometer versus thegyroscope may be an indication of an anomaly. For a cart in a parkinglot, passing vehicles may distort magnetometer data and the resultingheading estimate. An embodiment of a dead reckoning system can usegyroscope data to confirm the heading estimate based on magnetometerdata or combine magnetometer data with gyroscope data in headingestimates. Another embodiment of a dead reckoning system may beconfigured to perform heading estimates based only on gyroscope datawhen the system is in a busy parking lot, e.g., during peak shoppinghours.

In the more common type of shopping cart, the front wheels swivel oncasters and the axles of the rear wheels are rigidly fixed to the cartframe; thus, the cart's instantaneous motion vector (e.g., thederivative with respect to time of the track formed over time by thecart's center of mass) is normal to the line between the two rearwheels.

Explicit hidden variables in the state estimator for a longitudinalpitching motion and axial rolling motion may be useful to dead reckoningestimates. In the cart's coordinate system, yawing motion can beconsidered compensated by the front swivel wheels. The hidden variablesof a state estimator for the cart motion include the instantaneous 3-Dheading and the instantaneous speed in the frame-centered coordinatesystem. In situations where vibration data can be noisy, e.g., due to arotation detecting wheel in poor contact with the ground, one or morehidden state variables can be used to improve vibration analysisaccuracy. For example, a wheel having a flat surface portion but in goodcontact with the ground may produce data with a regular time-domainsignature from the flat surface coming in and out of contact with theground. An embodiment can use such data, for example, to filter the rollcomponent from vibration data. This may improve accuracy of vibrationanalysis. Another embodiment may be configured to use one or more ofsuch hidden state variables instead of performing vibration analysis indead reckoning. This may have the advantage in an energy-constrainedsystem because extracting a signature from a hidden state variable lessnoisy than corresponding vibration data may require fewer samples, lowersample rate, and/or less computation.

A physical effect which produces unreliable rotation information cansometimes affect the vibration signature. As a counterexample, a wheelwhich is completely not in contact with the ground (e.g., because thecart frame has been bent) may not have much effect on the vibrationsignature. As another counterexample, a wheel which has very poortraction, e.g., due to snow, ice, or sand on the ground, may not havemuch effect on the vibration signature. On the other hand, a wheel incontact but with heavy caster chatter can create a vibration signatureat the frequency of the caster chatter, and potentially at harmonicsthereof. An embodiment can distinguish the caster chatter frequency fromthe rotation frequency. The frequencies can be distinguished by 1)recognizing that the caster chatter frequency may typically be greaterthan the rotational frequency; and 2) using the estimate of the chatterfrequency provided by the magnetometer in the wheel in the searchalgorithm for vibration peaks—not associating peaks with characteristicsmatching the chatter frequency estimate with rotation frequency.

The practically achievable yaw rate (changing in heading or direction)of a human-propelled shopping cart may be less than ninety degrees persecond. A Kalman filter with observables including corrected three-axismagnetometer readings and a simple gravity vector can be sufficient tooutput heading information to sufficient accuracy. The latent variablesof the heading estimator can be the three-axis heading vector and theheading rate vector.

b. Reducing Error in Longitudinal Speed Estimation

As described above, longitudinal speed of a wheeled object can beestimated by measuring the rotation rate of one or more of the wheels.However, in some cases it may be advantageous to estimate thelongitudinal speed of the wheeled object by techniques other thancounting wheel rotations. For example, in the case of a retail storeshopping cart, it can be desirable to mount the magnetometer-basedcompass rigidly to the cart handle. Furthermore, for reasons of cost andease of logistics, it can be desirable that the entire electronicsassembly be mounted to the cart handle. Similar considerations apply toluggage carts such as those used in airports, train stations, etc., andother applications to other wheeled objects as well.

However, in many cases it can be a challenge to provide directmeasurements of wheel rotation to an electronics assembly which ismounted not on the wheel (e.g., to the cart handle) while simultaneouslyachieving both acceptably low cost (including relative ease ofinstallation, robustness and longevity in operational usage, etc.) andlong battery life for the wheel. Advantageously, for the longitudinalspeed estimation, a state estimator based not on wheel rotation data canbe used, e.g., an estimator based on accelerometer data.

However, low cost, low power MEMS accelerometers may not have propertiessuch that accelerometer output can simply be directly double integrated(first into velocity, with velocity then integrated into position) withacceptable accuracy to determine the position of the wheeled object.

For example, the KMX62 Tri-axis Magnetometer/Tri-axis Accelerometer,available from Kionix, Ithaca, N.Y., has a nominal accelerometer DCoffset error after calibration of 25 milligee or 0.25 m/sec². A onedegree error or change in the alignment of the accelerometer vertical(z) axis to the cart longitudinal (x) axis, as caused for example by thecart frame reversibly bending due to a heavy load being placed in thebasket, results in another 17 milligee error in longitudinalacceleration. Linearity errors from the accelerometer axis with thehighest vertical component can easily contribute many more milligees tothe longitudinal error depending on how the accelerometer axes aremounted relative to the cart's longitudinal axis. An uncorrected errorof 0.25 m/sec² in longitudinal acceleration will produce a positioningerror of 12 meters after a mere ten seconds through simple doubleintegration of the acceleration. Clearly this is not a viable solutionfor estimating the position of a wheeled object.

The longitudinal speed state estimator as described in this disclosurecan use vibration data to compensate for the accuracy limitations ofsuch low-cost, low-power accelerometers.

c. Example Constraints

For certain embodiments of the vibration-based state estimator, one ormore of the following constraints may be applicable: (1) The wheeledobject has a frame which is approximately rigid to within the neededaccuracy of motion estimation. (2) Quasi-random roughness in the surfaceon which the wheeled object travels (e.g., a floor or a parking lot) hasa size scale much smaller than the wheelbase of the wheeled object (andmay be much smaller than the diameter or circumference of the wheel).For example, the wheelbase of a cart can be about one meter or more (andthe wheel diameter, a few to 20 cm), and the quasi-random roughness of amoderately heavily worn asphalt parking lot is on the order of one tofive millimeters Root Mean Squared (RMS). The range of surface roughness(RMS) for many parking lots (asphalt or concrete) can be from about 0.1mm to 10 mm, 0.5 mm to 8 mm, 1 mm to 5 mm, or some other range. In somecases, the range of surface roughness (RMS) for many parking lots(asphalt or concrete) can be measured relative to the wheel diameter(D), and may range from about 0.001D to 0.1D, 0.01D to 0.05D, or someother range. (3) It may not be practical to obtain reliable rotationdata from a wheel which is in continuous, non-skidding contact with theground. In some implementations, where reliable wheel rotation data canbe obtained, the reliable wheel rotation data can be used additionallyor alternatively to the techniques described below.

To improve a continuous, non-skidding contact between a wheel and theground, the wheel may be comprise a suspension device, e.g., aspring-loaded caster. Such a device can be especially useful where theground is uneven, when the wheel is worn, and/or if the cart frame isbent.

d. Longitudinal Speed Estimation Via Vibration Analysis

An example filtered accelerometer time series (of one second duration)as measured at a shopping cart handle is shown in FIG. 8. The graph 800in FIG. 8 shows acceleration (in “g”s, where g is standard gravity) as afunction of time (in seconds) for three components of the acceleration,with x in the direction of forward (or, equivalently, rearward) cartmovement in the horizontal plane, y perpendicular to x in the horizontalplane, and z in the vertical direction (perpendicular to the surfaceover which the cart travels), as illustrated by coordinate system 230 inFIG. 2. Data in the graph 800 was measured on a somewhat rough asphaltsurface, using a typical grocery store shopping cart loaded with about15 kg in the main basket. Sampling rate was 20,000 samples per second(sps) using a 6 kHz bandwidth three-axis piezoelectric accelerometer(Measurement Specialties (Hampton, Va.) model 832M1 accelerometer). Theapplied filtering algorithm was 1-D median filter followed bySavitsky-Golay smoothing (order 3, window length 7) and detrending overthe displayed width. The root-mean-square (RMS) amplitude of thisparticular signal is about 1.4 g in the x axis, 1.2 g in the z axis, and0.7 g in the y axis.

FIG. 9 shows an example of the wheel rotation rate versus time profileof the same shopping cart under the same conditions. The wheel speed ismeasured by parabolic interpolation of the output of a precision Halleffect sensor sampled at 1600 sps (the raw speed, shown in thin line905). In an embodiment, the sample rate of the vibration data sensor canbe roughly 5 to 10 times the system bandwidth for the purpose of signalprocessing. A realistic system bandwidth can be 10 to 20 times themaximum wheel rotation rate (e.g., 100-200 Hz for a maximum wheelrotation rate of 10 cycles per second). The interpolated speed (1 secondmoving average) is shown by thick line 910. The rapid oscillation of thespeed in the raw speed data with frequencies in the tens of Hz is causedby small scale roughness in the asphalt surface. In this example, theestimated (e.g., interpolated) wheel speed is in a range from about 3.2revolutions per second to about 3.7 revolutions per second. As discussedherein, the linear speed of the wheel (and cart) is the speed inrevolutions per second multiplied by the circumference of the wheel.

FIG. 10A shows the Power Spectral Density (PSD) of the same data set,but calculated using Thomson's multitaper method as implemented in theMATLAB® Signal Processing Toolbox pmtm function. Other conventionalmethods for calculating the PSD (e.g., Welch's method) may not providesuitable PSD data, possibly due to the rapid oscillation in the rawspeed data (see, e.g., line 905 in FIG. 9). The horizontal axisrepresents frequency in Hz. The vertical axis represents PSD in g²/Hz inlogarithmic scale, units commonly used to measure vibration amplitude.

Referring to FIG. 10A, the X-axis is in the direction of motion of thecart, the Y-axis is perpendicular to the direction of motion andparallel to the surface over which the cart travels (e.g., in thehorizontal plane), and the Z-axis is perpendicular to the surface overwhich the cart travels (e.g., in the vertical plane). The frequency f0is the nominal rotation rate of the cart's wheels (assuming that all thewheels are of the same diameter as is usually the case; carts withmultiple wheel diameters may need additional processing), averaged overthe length of data capture interval. In other words, for N totalrotations over a time interval T, f0=N/T. In FIG. 10A, f0 isapproximately 3.9 Hz, which translates to a speed of 1.6 meters/secondor 3.5 miles per hour for a shopping cart wheel with a diameter of 5inches. The value of f0, of course, depends on the speed of the wheels.

The 5 dB width is the range of rotation frequencies centered on f0 suchthat 68% (1 standard deviation for normal distribution) of thefrequencies fall within the range [f0−0.5*BW_(5 dB), f0+0.5*BW_(5 dB)].Rotation frequencies can be calculated as the inverse of the intervalbetween the same phase point in two successive rotations.

FIG. 10B shows the same data as displayed in FIG. 10A, but in thefrequency range 1.5 Hz to 6.5 Hz, to make the spectral features nearf0/2 more visible. The nominal rotation rate can be determined throughthe presence of a strong peak and/or a weak peak in the PSD. A strongpeak can be defined as an amplitude at least, e.g., 5 dB greater thanany value of the given acceleration axis PSD to a distance of plus orminus, e.g., 3 times the 5 dB bandwidth of the rotation spectrum, wherethe 5 dB bandwidth is calculated as described above. For example, forthe data in FIG. 10B, the 5 dB bandwidth of the f0 signal is about 0.3Hz, so the f0/2 peak in the X axis at about 1.9 Hz is considered“strong” because is it more than 5 dB greater than any other peak overthe range 1.9+/−0.9 Hz. Weak peaks can be described as having amplitudesless than, e.g., 5 dB but greater than, e.g., 2 dB relative to theirlocal region in the PSD space (plus or minus 3 times the 5 dB bandwidthof the driving frequency). Different embodiments may use differentvalues for the amplitude and/or bandwidth parameters depending on cartand/or installation site characteristics. For example, one installationmay use 5 dB, 2 dB, and 3 times the 5 dB bandwidth as described above.Another installation may use 6 dB, 3 dB, and 4 times the 6 dB bandwidthinstead. Yet another installation may use 4 dB, 2 dB, and 3 times the 4dB bandwidth. Typically, increasing the search bandwidth may make iteasier to catch a relatively low peak in the vibration spectrum (e.g.,as may occur when the cart is jerkily accelerating or decelerating,which “smears” the peaks out), but may also increase the risk of a falsepositive (e.g., identifying a peak not caused by wheel rotation, forexample, a pseudo-harmonic because of some feature in the asphalt thathas constant spacing. The value of these parameters can be determinedduring the design phase, or during the installation of a site.

For the cart design corresponding to FIG. 10B, the most reliablediscriminant for detecting f0 is the presence of a strong peak at f0/2in the X axis acceleration spectrum along with the absence of a peak inthe Y and Z axes acceleration spectrum (indeed, a local near-minimum inthe Z axis acceleration spectrum), as shown in box 1070. A candidate f0value can be validated by the presence of a weak local peak at f0 in theY axis acceleration spectrum and at 1.5*f0 in the X axis accelerationspectrum (e.g., the first odd harmonic of the fundamental drivingfrequency at f0/2).

In an embodiment, once the dead reckoning system determines f0, theforward speed of the cart can be determined by multiplying f0 by thecircumference of the wheel. For example, for a US shopping cart wheelwith a diameter of 5 inches, the circumference is 15.7 inches (e.g., πtimes the diameter), and for the example value of f0=3.94 Hz determinedfrom the example PSD in FIGS. 9 and 10, the estimated forward speed ofthe cart is 61.9 in/s=5.16 ft/s=3.52 miles per hour=1.57 m/s.

Accordingly, embodiments of the dead reckoning system may utilizevibration sensor data to estimate a rotation rate of the wheel of awheeled object (e.g., a cart) and estimate a forward speed of the cartbased on the estimated rotation rate and a circumference of the wheel.The vibration sensor data can include a short time series ofacceleration data in one, two, or three directions. The short time canbe in a range from about ½ of a wheel rotation period to five to 10rotation periods (or more). For example, for certain carts the shorttime is in a range from about 0.1 to about 5 seconds. In situations inwhich valid rotation data is intermittently available, an embodiment canuse the periods when the wheel is in good ground contact to update thevibration signature. The directions for the acceleration data caninclude a first (forward) direction of the wheeled object, a seconddirection perpendicular to the first (forward) direction, and/or a thirddirection perpendicular to the first and the second directions. Forexample, the second direction can be in a horizontal plane (the plane inwhich the wheeled object is moving) and the third direction can be in avertical plane. The horizontal plane can be generally parallel to thesurface over which the wheeled object travels.

The dead reckoning system can estimate the wheel rotation rate based atleast in part on identifying a peak in an acceleration spectrumassociated with the acceleration data. The peak can be associatedacceleration data in the direction of motion of the wheeled object. Theestimated wheel rotation rate can be twice the frequency of the peak.Some implementations can validate an estimated wheel rotation rate bydetermining a presence of a second peak in the acceleration spectrum at1.5 times the estimated wheel rotation rate. Some implementations may,additionally or alternatively, validate the estimated wheel rotationrate by determining the presence of a third peak at the estimated wheelrotation rate in an acceleration spectrum associated with horizontalaccelerations of the wheeled object perpendicular to the direction ofmotion of the wheeled object.

The specific features to be extracted from the vibration spectrum may bedifferent for different shopping cart constructions (e.g. stainlesssteel wireframe cart basket versus plastic cart basket) and fordifferent applications or surfaces over which the shopping carts move.Vibration signatures in FIGS. 8, 10A, and 10B are an example for aparticular scenario.

Algorithms useful for feature extractions to obtain signatures include:(1) Bulk Fast Fourier Transform (FFT) at high spectral resolution,searching for clear harmonic content; (2) Discrete Fourier Transform(DFT) over a range of frequencies corresponding to the plausible rangeof the wheels' instantaneous angular velocities, searching for maximumenergy migration into plausible harmonic peaks. For many shopping cartapplications, the range of wheel angular frequencies is from about 1 Hzto about 5 Hz or about 1 Hz to about 10 Hz. (3) Time domain windowingmethods looking for impulse peaks (e.g. associated with flat spots onthe wheels).

For Bulk FFT, the minimum required spectral resolution can be derivedfrom the spectral width of features to resolve. For example, thespectral width of the f0/2 peak in FIG. 10B (1070) is about 0.1 Hz wide.To clearly resolve the peak may require about four to six (e.g., five)distinct frequency bins, for a required spectral resolution of 0.016 to0.25 (e.g., 0.02) Hz.

Clear harmonic content in the context of Bulk FFT can be defined interms of peaks and their harmonic ratios. Referring back to FIG. 10A, acandidate peak may be defined as one where three successive frequencybins at or near the center of the candidate peak, have an amplitude morethan 3 dB greater than any other value within a quarter octave rangecentered on the candidate peak (e.g., from candidate peak centerfrequency divided by the fourth root of two to the candidate peak centerfrequency multiplied by the fourth root of two) and more than 5 dBgreater than the RSS value of across the half octave range.

The nominal center frequency of a candidate peak can be defined viaparabolic interpolation in logarithmic amplitude of the highestfrequency bin within the candidate peak and the immediately lower andhigher frequency bins. Candidate peaks can be in a harmonic ratio if theratio of their center frequencies is an integer, e.g., 2 or 3, to withinthe precision set by two to three times the spectral resolution. For anoutdoor surface (e.g., asphalt), an embodiment may not considerharmonics higher than the third harmonic to be a candidate becausehigher harmonics may be too noisy. For a smooth indoor surface (e.g.,linoleum), an embodiment may consider higher harmonics as candidates.

In some cases candidate peaks may be additionally qualified by therelationships in candidate peaks between difference vibrational axes.Referring back again to FIG. 10B, the f0/2 peak (1070) is characterizedby the combination of a high prominence peak in the X axis with theabsence of a peak in the Y or Z axis at the same frequency, while the f0peak (1080) is characterized by a peak in the Y axis and the absence ofa defined peak in the X and Z axes. Peak in the Y axis at f0 may not beconsidered a candidate peak by the criteria described above, since thepeak amplitude of −27.4 dB (g2/Hz) at 3.77 Hz is only 2.8 dB above thepeak amplitude at 4.16 Hz. More elaborate peak-finding algorithms can beused. Such an algorithm can locate peak in the Y axis at f0, e.g., bycomparing the peak amplitude of the peak to the RSS amplitude of the twohighest values in the quarter octave range rather than to the highestvalue; by that criterion peak in the Y axis at f0 can be recognized.

e. Longitudinal Speed Estimation via Acceleration Analysis—ConcreteJoint Example

An example accelerometer time series as measured on a shopping cartrolling on concrete flooring is shown in FIGS. 11A and 11B. The cartunder measurement contains about 15 kg of payload. The cart rolls acrosstwo concrete expansion joints in a fairly straight line. Plot 1100 showsacceleration in the vertical axis (e.g., the Z axis) versus time. Theburst of vertical acceleration at t=1.0 and t=1.5 and then at t=5.8 andt=6.3 are results of the front and rear wheels, respectively, hittingthe expansion joint. The greater amplitude of the second burst (at t=1.5and 6.3) are results of the rear wheel on this cart not being castered,and hence without a shock absorbing effect of the caster as there is onthe front wheel. A cart crossing an expansion joint at a significantangle may have up to four different events, one for each wheel of afour-wheel cart. With knowledge of the spacing between concreteexpansion joints and the time it takes for a cart to cross successivejoints (e.g., 6.3-1.5=4.8 seconds in plot 1100), the speed of the cartcan be estimated.

FIG. 11B shows a zoomed-in plot around t=6.3 second corresponding toFIG. 11A. t=6.3 second corresponds to the time when the rear wheels hitthe second concrete expansion joint. Plot 1150 shows the Z accelerationgoing negative at t=6.319. This corresponds to the rear wheel droppingover the first edge of the expansion joint. The strong peak at t=6.323corresponds to the time when the wheel hits the bottom of the joint.Plot 1150 shows the peak acceleration in the Y axis lagging thesimultaneous peak in Z and X by about 1 millisecond. This lag may be dueto the cart swaying because of not hitting the expansion joint exactlystraight on.

f. Example State Estimator

An embodiment can implement a state estimator that is a linear quadraticestimator (LQE—a standard Kalman filter). However, the disclosure is notlimited to LQEs. Other implementations may involve a combination of ahidden Markov model and continuous latent variable estimation (such asan extended Kalman filter, unscented Kalman filter, etc.).

Available observables for the continuous estimator can include:

A three-axis accelerations of the body frame of the cart, which can becoupled to an electronics system, measured by a moderate bandwidth (e.g.up to about 100 Hz) DC coupled three-axis accelerometer. An exampleaccelerometer is the accelerometer system of the FXOS8700CQ digitalsensor and 3D accelerometer, available from Freescale Semiconductor.Another example is the 3D accelerometer system of the KMX62 tri-axismagnetometer/tri-axis accelerometer, available from Kionix, a Rohm GroupCompany (Kyoto, Japan).

A three-axis magnetometer readings, which can be in the same referenceframe as the accelerometer. An example magnetometer is the one includedin the Freescale FXOS8700CQ digital sensor and 3D accelerometer. Anotherexample magnetometer is the one included in the KMX62 tri-axismagnetometer/tri-axis accelerometer. In some embodiments, theaccelerometer and the magnetometer can be separate components.

Features extracted from the high frequency, AC-coupled vibrationspectrum of the cart frame, which can be coupled to the electronicssystem but not necessarily coupled via the same circuitry as theaccelerometer. The features can include the estimated wheel rotationrate f0. The number of independent axes of vibration measurement candepend on the mechanical construction of the cart. For example, it maynot be accurate to assume that the three Cartesian axes of vibration areindependent at high frequency.

Types of sensors for measuring vibration that may be appropriate to thisdisclosure include (1) a cantilevered piezoelectric beam with optionalpoint masses to tune the response spectrum; (2) a small magnet on acantilevered beam of nonmagnetic material, e.g., stainless steel,operating within the elastic limit of the beam, with optional pointmasses to tune the response spectrum, e.g., by inducing anelectromagnetic force (EMF) in a coil; (3) a cantilevered magnet plussense coil, which can be a small, cheap, and low power component set fora high bandwidth vibration sensor; (4) a high bandwidth MEMSaccelerometer, e.g., KX123 (available from Kionix, Ithaca, N.Y.).

As shown in section titled Longitudinal Speed Estimation via VibrationAnalysis and FIGS. 10A and 10B, the bandwidth of the vibration sensormay not be critical in some implementations. For example, there are nocomponents of interest above about 15 Hz in the example data in FIG.10A. However, a high sample rate can be used to provide sufficientfrequency resolution over fairly short time periods, e.g. when thecart's rotational speed is changing.

g. Heading Estimation

FIG. 12A shows an example method flowchart 1200 by which an embodimentof the dead reckoning system can determine an estimated heading in thecoordinate system of the wheeled object (e.g., coordinate system 230).

Flowchart 1200 can start at block 1206, wherein themagnetometer/accelerometer can be compensated for offsets/errorsresulting from a plurality of factors. Calibration data can comprise thegain, offset, and nonlinearity of each sensor axis as a function oftemperature 1210. An embodiment may calibrate all axes of both theaccelerometer and the magnetometer. Another embodiment may not calibratethe horizontal axes (e.g., x and y axes in coordinate system 230) forthe accelerometer. For example, for the Kionix KMX62, the accuracy ofthe dead reckoning solution may not be affected significantly by errorsin the accelerometer. On the other hand, the change in offset and gainof the magnetometer axes over temperature may significantly affect theaccuracy of the dead reckoning estimates. Accordingly, an embodiment cancalibrate each axis of the magnetometer over temperature individually. Asystem with a magnetometer whose characteristic does not varysignificantly over temperature or an installation with operatingtemperatures over a narrow range may not need individual calibration ofeach axis of the magnetometer.

With some sensor types, including the Kionix KMX62, the magnetometeroffsets can change significantly after being exposed to the hightemperatures of the solder reflow process (e.g., about 260° C. accordingto IPC/JEDEC J-STD-020C). Thus, the sensors can preferably be calibratedafter the PCBA has been assembled, e.g., during a post-assemblyproduction test process. During calibration, the database “calibration(gain+offset+nonlinearity versus temperature)” 1210 can be created. Thedatabase can be stored in the flash memory of the processor, e.g.,memory 425 in FIG. 4. When calibration is applied at block 1206, atemperature sensor can provide temperature data 1202, themagnetometer/accelerometer can provide their raw measurements 1204, andthe database 1210 can provide calibration data. The raw measurements1204 can be in the coordinate system of the accelerometer/magnetometersensor package.

Magnetometers typically have a nonlinear response to the appliedmagnetic field over the field strengths of interest (e.g., from −100 to+100 μT). Taking the KMX62 as an example, the worst case error over thatfield range is around 2%. The factory calibration process can provide,on a per magnetometer basis, the actual curve for each axis, e.g.,output voltage=offset+gain*applied_field+F_nonlinear_error(appliedfield).

An embodiment can invert the nonlinear error function into a lookuptable and store the table in a memory as part of the factory calibrationprocedure. At runtime, the system can look up the true field as afunction of both the magnetometer output and the temperature sensoroutput. Accordingly, the output of block 1206 can betemperature-compensated and linearized magnetometer/accelerometerreadings.

At block 1208, the system can rotate the temperature-compensated andlinearized readings to the cart's coordinate system, e.g., coordinatesystem 230. This rotation provides measurements in the cart's body framecoordinate system. The database “PCBA to cart frame angles” 1212 can bepopulated during or after the installation of the dead reckoning systemonto the cart, e.g., by putting the cart on a known level surface andreading out the accelerometers' DC values.

At block 1214, the system can apply digital filters to produce filtered,noise-reduced measurements. The applied digital filters can havefrequency response curves which vary with the current estimated cartspeed or wheel rotation rate 1218. In some embodiments, the applieddigital filters may have fixed frequency response curves. In anembodiment, each filter (e.g., per rotated axis) can be a two-polelow-pass Chebyshev filter, with the cutoff frequency lower than half ofthe rotation rate to suppress vibration noise at f0/2 (see, e.g.,reference 1070 in FIG. 10B) but not being too low to cause a slowresponse to the cart actually turning (e.g., too low a cutoff frequencycan cause the heading estimate to lag the true heading, which in turncan cause dead reckoning errors). An example cutoff frequency can be thecurrent rotation rate times 0.375, 0.4, 0.425, etc.

At block 1216, the system can combine the magnetometer and theaccelerometer data, producing cart heading in geomagnetic fieldcoordinates, e.g. North-East-Down (NED) coordinates. The database “Hardand soft iron compensation” 1220 can be created after the dead reckoningsystem is installed on the cart. One way to generate database 1220 is tospin the cart around its vertical axis (e.g., z axis in the coordinatesystem 230) a few times. Another way to generate the database is usingsome fixtures suitable for the purpose.

Instead of the flow shown in FIG. 12A, an embodiment can implement analternative flow for heading estimation. For example, a processing unit,e.g., processor 425, can read data from the one or more accelerometers.The embodiment can transform the accelerometer data to cart framecoordinates, e.g., coordinate system 230. This can provide an estimateof tilt at the current location and a reference frame for themagnetometer output. The system can read data from the one or moremagnetometers. The embodiment can correct for hard and soft irondistortion. The correction can be computed based at least in part oniron distortion correction constants stored in memory associated withthe processor. The system can also filter to remove or reduce noisecaused by the local power line frequency, as described in the sectionabove entitled Reducing Error in Heading Estimation. The heading can berelative to the geomagnetic field where the wheeled object is located.Correction of estimated accelerometer alignment and offsets can reduceerror in this transformation.

h. Steady State Speed Estimate Update Loop

FIG. 12B shows an example method flowchart 1224 by which the deadreckoning system can determine an estimated position of the wheeledobject (e.g., shopping cart).

FIG. 12B can start from block 1228, wherein the processor can obtaincart heading data in NED coordinates. The cart heading data can bederived from flowchart 1200 in FIG. 12A, the alternative embodimentdescribed above, or some other method. At block 1232, the processor canupdate velocity vector estimate, illustrated as data block 1272, fromthe one or more accelerometers. At block 1236, the processor can updateyaw estimates from accelerometer data. At block 1240, the processor cansearch the power density spectrum of vibration data for spectral peaksto determine the most probable frequency of wheel rotation and hence thespeed of the wheel. This can be done, for example, using the methoddescribed above in the section titled Longitudinal Speed Estimation viaVibration Analysis. The time series of vibration data, illustrated asdata block 1276, may be stored in a ring buffer such that old data isautomatically overwritten with new data. The size of the ring buffer canbe dependent on the length of the time series data needed for thevibration analysis.

At block 1244, the processor can determine whether a plausible frequencyof wheel rotation is found through the analysis, for example, by findinga spectral peak of the X axis acceleration data at a first frequency andfinding another spectral peak of the Y axis acceleration data at thethird harmonic of the first frequency, as explained above in the sectiontitled Longitudinal Speed Estimation via Vibration Analysis. If aplausible frequency is found, the process proceeds directly to block1252. Otherwise, the process proceeds to block 1252 through block 1248,wherein the rotation rate search bounds can be widened for the nextiteration to improve the likelihood of finding a plausible frequency.

At block 1252, the processor can update velocity estimate andaccelerometer offsets. The velocity estimate can be based on estimatedheading as determined in block 1228 and speed estimate as determinedbefore block 1252. The velocity estimate can be used to update datablock 1272. The accelerometer may have time-varying offsets. Theseoffsets can change slowly and can be derived as a constant for theduration of one iteration of loop 1224. For example, an embodiment candetermine accelerometer offset during a time interval using wheelrotation data in the same time interval, which provides a measurement ofspeed and hence of acceleration, e.g., the difference between measuredspeed in the current iteration versus the last iteration. Someembodiment may update accelerometer offsets for time intervals in whichgood wheel rotation data is available, and not update the offsets fortime intervals in which the wheel rotation data is noisy.

At block 1256, the processor can propagate velocity estimate to producea position estimate, e.g., data block 1280. This propagation cancomprise, for example, summation of time series of velocity data and canvelocity vector estimate 1272. At block 1260, the processor candetermine whether position-dependent steps are needed. If yes, theprocess proceeds to block 1268 through block 1264, wherein the processorcan execute position-dependent steps. Otherwise, the process proceedsdirectly to block 1268. At block 1268, the processor can wait until thenext iteration starts and repeat the process from block 1228.Position-dependent steps can include, for example, initiating a warningsequence if the cart is in a warning zone.

For the purposes of illustration and simple explanation, FIG. 12B isdrawn as a sequential process. In some embodiments, some operations,e.g., the input/output (I/O) operations such as reading theaccelerometer and magnetometer, can be overlapped or performed inparallel.

i. Ongoing Magnetometer Calibration

There are at least three sources of error in a cart heading derived frommagnetometer readings for a dead reckoning system: 1) errors in themagnetometer sensor itself. With such errors, the sensor reading is notthe true value of the magnetic field at the exact location of the sensor(e.g., what would be output by an infinitely accurate magnetic fieldsensor sampling at the exact same time and location as the actualmagnetometer in the dead reckoning system); 2) errors in the estimate ofhow the true magnetic field at the sensor is related to the knowngeomagnetic field, e.g., distortions caused by magnetically activematerial in the near vicinity of the magnetometer. The standard term ofart for this is hard iron and soft iron errors, hard iron being materialthat has a permanent magnetic moment in the absence of an externallyapplied magnetic field, and soft iron being material without a permanentmoment but which magnetizes in the presence of an applied field; and 3)errors in the estimate of the relationship of the magnetometercoordinate system to the cart frame coordinate system.

For certain specific magnetometer types, including the implementationwithin the Kionix KMX62, that error 1) can be basically fixed after PCBAreflow for any given individual magnetometer (e.g. the specific KMX62 ona given PCBA), within certain constraints of temperature and appliedmagnetic field. For the KMX62 the exposure limits within which the gainand offset do not permanently change are >125° C. and 500,000 μT,conditions which the cart would not experience in operation. Thecorrection of error 1) corresponds to block 1206 in FIG. 12A. Thesection below titled Example off-Line Calibration contains additionalrelated descriptions.

Error 3) can be caused, for example, by the cart handle being bent viaabuse, or the angle of rotation of the dead reckoning system about thecart handle axis being changed. Block 1208 in FIG. 12A can provide thecorrection to rotate the sensor outputs to match the cart coordinatesystem, but the database that block 1208 uses (block 1212) is normallyset once after the system is installed and then not updated inoperation. If the data in block 1212 become inaccurate because of, e.g.,the abuse mentioned above, accuracy of the dead reckoning system maylikely decrease.

An embodiment can detect the probable cases of significant change inblock 1212 by the fact that when the cart is dead stop on a known levelsurface, the rotated accelerometer readings is expected to be one geedown and zero gee north or east. If they are not, an embodiment cancorrect the rotation matrix 1212 such as to produce the correct output.

The remaining problem for heading accuracy is that error 2) can and doeschange over time, e.g., dynamically due to a large vehicle passing by.In particular, many shopping carts are made out of ferromagneticmaterial (e.g. mild steel). Residual magnetization of such material canchange over time (e.g., if a cart is stored over a long period of timein a particular orientation, the magnetic domains can slowly align inaccordance with the magnetic field the cart experiences). The changingmagnetization of the cart can cause errors in the estimated heading,because the magnetic field being measured by the magnetometer may likelybe different from the geomagnetic field.

A standard solution to this general problem, when highly accuratecompasses are needed (e.g., for ship or aircraft navigation in thepre-GNSS days) is to periodically align the thing to which the compassis mounted (ship or airplane) to a series of pre-surveyed knownheadings, observe the compass reading at each of those pre-surveyedheadings, and note the compass error at each. The standard term forthis, during the Second World War and earlier, was a compass deviationcard, which was a handwritten, frequently updated list of the compasserrors.

A standard solution for devices like smartphones is to force the user torotate the device multiple times over all three axes, measuring thethree axis magnetometer outputs all the while. If the magnetometer wereperfect and there were no error 2), the cloud of points described by thethree-axis magnetometer output would all be on the surface of a sphere.In practice, however, because of errors 1) and 2), the cloud of pointsforms an offset ellipsoid. The cloud can be processed to form estimatesof errors 1) and 2). The standard term for this is hard iron and softiron correction. This process is described in the art, e.g., inFreescale Application Note AN4246, “Calibrating an eCompass in thePresence of Hard and Soft-Iron Interference.”

However, there are some difficulties applying this standard solution toa magnetometer mounted on a wheeled object such as the shopping cart: 1)it requires the magnetometer, as installed, to be rotated over threeapproximately orthogonal axes. Doing that three-axis rotation with ashopping cart may not be easy; 2) because this standard solution doesnot involve temperature compensation, the calibration is only valid overa small temperature range. For devices like smartphones, this may notpresent a concern because even the best smartphone compass calibrationrarely produces an accuracy that can be affected by small errors causedby short term drift over a modest temperature range. But for the usageapplications based on this disclosure, a much higher degree of compassaccuracy over a wide ambient temperature range, e.g. −15° to 50° C., isdesired; 3) the process has to be repeated if the external magneticinfluence (error #2) changes, which can be dynamic as noted above.

Advantageously, an embodiment according to the present disclosure canovercome these difficulties. A dead reckoning system according to thepresent disclosure can have the true value of the geomagnetic field atthe location where the system is installed (e.g., from Table 1, Index 2in section below titled Example Site Configuration File) and canseparately compensate for error 1) as described above.

A shopping cart normally only rotates about its Z axis, which is usuallywith a few degrees of vertical. To initially populate data in block 1220of FIG. 12A, the installer can deliberately spin the cart around the Zaxis in an area where the magnetic field can be trusted to be very closeto the geomagnetic field, e.g., outdoor and not too close to any largeferromagnetic objects (e.g., at least three to five meters from a largesports utility vehicle and two to three meters from a car). Theinstaller may spin the cart one, two, three or more times. The set ofpoints which are output from block 1214 in FIG. 12A can form a thinslice near the equator of an ellipsoid (e.g., if the cart is perfectlylevel and there is no error 2), the points would form a perfect circle).With information on the actual magnitude of the horizontal component ofthe geomagnetic field, an embodiment can solve for both soft and hardiron effects on the cart's XY plane. It may be possible in theory tosolve for hard and soft iron on all three axes by deliberately spinningthe cart on a non-level plane, but in practice the extra potentialaccuracy in the heading estimate may not be worth the effort.

After block 1220 is populated as described above, the cart can be putinto service. In operation, an embodiment can continuously (e.g.,periodically) monitor the output of process 1214 during periods when thesystem knows the cart is outside (because the geomagnetic field isgenerally quite distorted inside buildings). If at any time the systemobtains a sufficient number (e.g., 5, 10, or more) of adequately spreadheading points (these points have already been heavily low pass filteredby block 1214) over a sufficiently short period of time (e.g., a fewminutes, less than 30 minutes, less than 1 hour), the system canre-execute the process described above after initial installation.

If the hard and soft iron calibration calculated by this operationalprocess is significantly different from the value stored in block 1220,the system can update the value of 1220. The updated value enables thesystem to compensate for error 2) which may be changing over time.

What may constitute a “sufficient number” of distinct heading points“adequately spread” over a sufficiently short period of time can be atthe discretion of a system designer. One example implementation has thefollowing:

The system examines a sliding window of the past 10-20 (e.g., 16)seconds worth of points and bins those points into four magneticquadrants in the horizontal plane (+X +Y, −X +Y, −X −Y, +X −Y). If atleast 10% to 15% (e.g., 12.5%) of the points are in each quadrant, andat least two quadrants each contains at least 25% of the points, thesystem may consider the points to be adequately spread.

Using the existing value of the hard and soft iron compensation matrix1220, if the vector magnitude of the geomagnetic field associated withany of those points is significantly different from the knowngeomagnetic field, the point can be rejected on the grounds that it wasprobably taken near some distorting external ferromagnetic object. Thisis a bootstrapping process—the initial calibration process to populate1220 should preferably occur in a known magnetic field (e.g., thegeomagnetic field at the location of the cart), but afterward the systemcan use existing value of data in block 1220 to know when the system isgetting valid data for recalibration.

Another embodiment may not attempt to recalibrate hard and soft ironunless a certain number of points (e.g., all but those at or below athreshold such as 0%, 1%, etc., over the sample 10-20 seconds) indicatean absence of external distortion—fewer points than the threshold arerejected for being significantly different from the known magneticfield.

1. Shopping Carts with Adjustable Child Seats

Some shopping carts include a user-adjustable child seat that can bemoved between a position where the child seat is closed and a positionwhere the child seat is open, permitting a shopper to place a child (orother items) on the seat portion. With reference to FIG. 16A (describedfurther below), this figure shows an example of a cart 1600 in which achild seat 1620 is in the closed position (which is sometimes referredto as child seat up, because the child seat portion is substantiallyvertical). In many carts, the shopper can push a metal frame of thechild seat 1620 away from a handle 1610 of the cart 1600, which causesthe seat portion to move to a horizontal position (e.g., the seatportion rotates down from the vertical position of FIG. 16A to thehorizontal position). The open position is thus sometimes referred to aschild seat down. FIG. 16B shows a shopping cart 1600 with the child seat1620 in the open or child seat down position. In general use, it hasbeen found that a majority of shoppers operate carts with the child seatdown, which permits a child, a purse or shopping bag, or store items tobe placed on the horizontal seat portion. Further, it has been foundthat the position of the child seat (e.g., up or down) typically doesnot change during a single navigating trip by the shopper.

When the child seat is up (in the closed position, e.g., FIG. 16A), themetal frame (often steel) of the child seat is relatively close to thehandle 1610 of the cart 1600 and thus may be relatively near to themagnetometer of the smart positioning system 1605 mounted to the carthandle 1610. When the child seat is down (in the open position, e.g.,FIG. 16B), a substantial part of the child seat is farther away from themagnetometer of the handle-mounted smart positioning system 1605. Thus,the amount of magnetic interference of a partially magnetized, metallicchild seat on the magnetometer is generally measurably different betweenthe child seat up and down positions. If the differing amounts ofmagnetic interference between the child seat up and down positions arenot calibrated for, heading errors of several degrees to tens of degreesor more may be introduced into the navigation procedures, leading toinaccurate dead reckoning positions.

For many shopping carts, the heading error is typically approximately asinusoid, with a maximum error at about 90 and 270 degrees heading. Themetal seat typically is constructed out of ferromagnetic wires where theindividual wires are aligned mostly left to right, e.g., along theY-axis according to the cart coordinate system 230 shown in FIG. 2.Thus, when the cart is heading in one of those directions (e.g., 90 or270 degrees magnetic heading), the geomagnetic field induces thegreatest field distortion in the metal seat. The amplitude of theheading error sinusoid can be as much as 90 degrees for an intenselymagnetized cart, but a more typical value is about 20 to 30 degrees (sothe root sum of squares (RSS) value of the error for a uniformlydistributed true heading is about 0.5*maximum error at 90/270 degreesheading).

Examples of techniques for calibrating magnetometers in carts havingadjustable child seats are described below. Some such techniques mayutilize two different hard/soft iron calibrations: one for when thechild seat is up and another for when the child seat is down. Use ofthese techniques can reduce cart heading error associated with the seatbeing up and near the magnetometer to about 2 to 3 degrees.

The following is an example of a dual calibration implementation for ashopping cart with an adjustable child seat. At installation time (or atanother calibration time), the installer can spin the cart around the Zaxis two (or more) times: at least once with the child seat up and atleast once with the child seat down. The data reduction from raw data topopulating the hard/soft iron compensation data for block 1220 of FIG.12A can be based on whether the child seat was up or down during eachspin of the cart. Thus, two sets of hard/soft iron compensation data canbe generated and stored at block 1220: one for the child seat upposition and one for the child seat down position. If the cart had morethan two operating configurations, compensation data for some or all ofthese configurations can be stored at block 1220.

During navigation, block 1216 of FIG. 12A can be performed as follows.As the cart navigates, the system can operate with a default hypothesisregarding the child seat position. In some implementations, the defaulthypothesis is that the child seat is open (child seat down). As the cartbegins navigating at an exit (e.g., state 520 of state diagram 500), thesystem can compare the heading calculated based on the current childseat position hypothesis with the heading calculated based on thenegation of the hypothesis.

On leaving the exit, the cart heading is (generally) known to be withina 180 degree arc of the direct path through the exit (e.g., as will bedescribed further with reference to FIG. 14, a ground plan 1400 caninclude a compass orientation of each exit). In many cases, only onechild seat position hypothesis will turn out to be consistent with aplausible cart direction (e.g., the measured magnetic field vector astransformed by the hard and soft iron compensations, which are thenprojected onto the cart's local horizontal plane). If both seat positionhypotheses are plausible, the system may execute the navigationalgorithm twice, once with each seat position hypothesis, until onehypothesis fails (for example, if the cart changes heading very much,e.g. by more than about 60 degrees, one of the two position hypothesestypically becomes impossible, namely, the magnetometer measurements donot correspond to any possible heading of the cart given one seatposition hypothesis).

In some embodiments, the system can use the foregoing procedure todynamically estimate whether the child seat is in the up position or inthe down position. For example, if the navigation algorithm is executedtwice, and fails for one of the hypothesized seat positions, then theother hypothesized seat position must be true, and the system canaccordingly dynamically update the navigation to reflect the deducedtrue position of the child seat.

These techniques are not limited to shopping carts with child seatsadjustable between an up and down position. These techniques aregenerally applicable to any type of cart having multiple operatingconfigurations, where the magnetic influence of cart materials on themagnetometer may be different in the different operating configurations.Different soft/hard iron calibrations can be generated for some or allof the operating configurations and used to reduce heading errorsinduced by the different magnetic interference experienced by themagnetometer in the different configurations.

j. RSSI-Aided Dead Reckoning

Dead reckoning estimates of absolute position can become increasinglyinaccurate as error accumulates through successive estimates. Estimatesof incremental position changes through dead reckoning, on the otherhand, can be fairly accurate where the method is carried out correctlywith sensors of sufficient accuracy. As described above, the accuracy ofabsolute position estimates through dead reckoning can be improvedthrough position reset using a precision position fix, such as signalsfrom an exit marker and/or an RF beacon. The accuracy of absoluteposition estimates through dead reckoning may also be improved throughincorporating other observables, e.g., RSSI, in the estimate process.

RSSI can provide an estimate of the distance between a transmitter,e.g., an access point 136, and the receiver, e.g., a dead reckoningsystem. Referring to FIG. 13, a single RSSI measurement may indicatethat the dead reckoning system is somewhere on the circle, e.g., 1310,of a certain radius (the distance indicated by the RSSI measurement)away from the access point. A series of RSSI measurements can indicatethat the dead reckoning system is somewhere on one of the concentriccircles at each measurement time.

FIG. 13 illustrates this concept. As shown, a series of four RSSImeasurements may indicate that the dead reckoning system is on circle1305 at the time of the first measurement, on circle 1310 and the timeof the second measurement, etc. The dead reckoning system may compute anincremental position change between the first and the secondmeasurements to be D₁ meters at X degrees (from 1325 to 1330). The deadreckoning system may further compute an incremental position changebetween the second and the third measurement to be D₂ meters at Ydegrees (from 1330 to 1335), and D₃ meters at Z degrees between thethird and the fourth measurement (from 1335 to 1340). There may only beone (or a plurality of—less likely with a longer series) set of pointson the concentric circles which satisfy the series of measureddistance/angle changes. Thus, in theory, the estimates of incrementalposition changes plus distances or radii indicated by RSSI can be usedto determine the absolute position of a dead reckoning system. Byeliminating accumulated errors in dead reckoning, such estimates may bemore accurate than absolute position estimates through dead reckoningalone.

In practice, both RSSI and dead reckoning estimates can have errors andranges (e.g., a range with normally distributed confidence level).Accordingly, the estimates of incremental position changes plusdistances or radii indicated by RSSI may not provide absolute positionestimates with pinpoint accuracy. However, such estimates can still beused to improve the accuracy of absolute position estimate through deadreckoning because the RSSI can increase the number of observables in (orcan place additional constraints on) the estimate.

Heading estimate supplied by a dead reckoning system, together withinformation on the location of the access point, e.g., from a siteconfiguration file, can be used to improve accuracy of RSSI. Forexample, the antenna receiving the access point signal may not have ahemispherical antenna pattern. The heading estimate and locationinformation can be used to compensate directional gain of the antenna,increasing the accuracy of RSSI.

Similar improvements may also be achieved through the use of otherobservables. The disclosed concept is not limited to an application ofRSSI. Increased accuracy of position estimates can provide the benefitthat position reset points, e.g., RF beacons, can be spaced furtherapart. This can reduce total system cost, or improve compliance withlocal code (e.g., local government ordinance and/or landlord rules)imposing constraints on installations and/or locations of transmitters.

V. Example System Implementation—Shopping Cart Containment

a. Example System Site

FIG. 14 shows an example of a ground plan 1400 of a retail store systeminstallation. The ground plan comprises the following: (1) an area(“Store interior”) 1410 where a cart's navigation behavior can bedifferent (e.g., not tracking position at all, except for detecting thatthe cart has entered or exited the store interior; tracking dwell time(merchandise aisles/shelves where consumers spend much or little time));(2) a containment boundary 1420 which may not be permissible for thecart to cross. The containment boundary is in turn defined by the set ofedges between an ordered set of vertices (six vertices 1425 in FIG. 14),and may form either an open or closed polygon; (3) entrances and exits(in this particular example, two exits 1415 which also function asentrances). Physical barriers can prevent carts from entering or leavingthe store other than through an entrance or exit; and (4) identifiedsections 1430 of, e.g., concrete, as distinguished from a differentsurface type, e.g., asphalt 1440. As discussed above, shopping cartcontainment is one possible application for the disclosed technology butother applications are relevant as well (e.g., tracking or monitoringluggage or warehouse carts, utility carts, etc.). FIG. 14 uses ashopping cart containment application for illustration, not by way oflimitation. Further, as described below, plans for floors other than aground level can be generated and used for cart containment andnavigation purposes in multi-level structures.

The coordinate system, for simplicity, can be referenced to the majoraxes of the store. The <x,y> coordinates of each relevant feature can bedetermined relative to the center point 1405 of the front face of thestore in this particular example. In some embodiments, the choice of<x,y> coordinate system can be made for the convenience of theinstallation design (e.g., referenced to architectural plans or propertyboundaries which may determine some of the containment boundaries).

Store exits 1415 are bidirectional in this particular example, that is,carts are permitted to enter and leave the store through eitherexit/entrance. In some embodiments, a store's interior may be designedsuch that certain portals are only permitted to be entrances or onlypermitted to be exits.

b. Example Site Configuration File

Table 1 shown below includes an example version of the siteconfiguration file which corresponds to the example ground plan 1400. Insome embodiments, the master copy of the site configuration file can bemaintained in the site controller 1435. In some embodiments, the siteconfiguration file can be transmitted to the navigation systems viatheir communication system, e.g., wireless RF techniques such asBluetooth Low Energy (BLE).

In some embodiments, the configuration file can be created during theinstallation design process as described in section titled ExampleInstallation and Calibration. In some embodiments, the configurationfile of an operational system can be updated based on changes after theinitial installation. A configuration version and/or a configurationtimestamp (e.g., a date) can be included in the site configuration file.An embodiment of a navigation system can determine whether to request adownload of the current version of site configuration file from the sitecontroller based on the values of configuration version and/or timestampfield (collectively “version number”) in the site controller's versionversus the navigation system's local version. The site controller canbroadcast its master version number periodically. This canadvantageously reduce energy consumption associated with updating thesite configuration file. In another embodiment, each parameter in themaster site configuration file can have an associated version number.The navigation system can transmit the version number of its localversion of site configuration file to the site controller. The sitecontroller can parse through the master site configuration file and cantransmit to the navigation system only those parameters with a versionnumber later than the navigation system's version number. This too canadvantageously reduce energy consumption associated with updating thesite configuration file.

In Table 1, attributes which are in italic type are those which may bedetected and/or updated during the learning process in this example. Forinstance, during site installation or during operation, a navigationsystem may detect a vibration signature associated with concreteexpansion joints at certain coordinates. The navigation system canderive parameters such as spacing and/or width associated with theexpansion joints, using its estimated position obtained via, e.g., deadreckoning and/or precision position fix. As another example, anavigation system may detect a vibration signature associated withasphalt at certain coordinates. The navigation system can deriveparameters such as roughness or coordinates of the boundaries associatedwith the asphalt surface. The navigation system may update its memory,e.g., in the site configuration file, with such updated information.

This learning process may take place over time. For example, detectingexpansion joints at certain coordinates, e.g., in concrete section 1,may be the start of a learning process. Over time, as the navigationsystem has traversed through the entire area of concrete section 1, itcan determine the spacing between the joints. In some embodiments, thenavigation system can upload the information acquired during thelearning process to a central processing unit for the site. For example,an embodiment can transmit the information through a communicationsystem 330 to the system configuration and control device 390, asillustrated in FIG. 3. The central processing unit can be configured toprocess the new information and integrate it with its master version ofground plan and/or site configuration file. The central processing unitcan be configured to download the new information to other navigationsystems. The upload/download can occur at a choke point where theshopping carts are expected to pass, e.g., an entrance and/or an exit.Different embodiments may include different sets of attributes to bedetected and/or updated during the learning process.

An embodiment of a navigation system can adapt its processing algorithmsbased on the ground plan as described in the site configuration file.For example, the navigation system may use different vibration analysisalgorithms for different surface types (e.g., concrete, asphalt, indoor,etc.) and/or for different roughness factor for a particular surfacetype.

TABLE 1 Example Site Configuration File Content Index Item Attribute:value Attribute: value 1 Site name: YourStore #42 location: <latitudelongitude> WarningDistance: 5 feet UnlockPolicy: CommandOnlyMainsFrequency: 60 Hz Configuration version: 7 Configuration date:xx-xx-201x 2 Geomagnetic coordinate system orientation: strength: 49 μTesla field 30° inclination: 59° declination: 13° 3 Exit # of exits: twostructure 3.1 exit A coordinates: <−45,1> exit direction: 180° detectiontype: magnetic, code 1 exit/entry type: both directions 3.2 exit Bcoordinates: <45,1> exit direction: 180° detection type: 8 kHz, code 2exit/entry type: both directions 4 Containment # of containmentvertices: 6 4.1 vertex 1 coordinates: <60,70> close with next vertex:yes 4.2 vertex 2 coordinates: <90,70> close with next vertex: yes 4.3vertex 3 coordinates: <90,−75> close with next vertex: yes 4.4 vertex 4coordinates: <−115,−75> close with next vertex: yes 4.5 vertex 5coordinates: <−115,0> close with next vertex: yes 4.6 vertex 6coordinates: <−60,0>: close with next vertex: no 5 Surfaces # ofstandard surfaces: 2 5.1 Standard Surface type: asphalt roughnessfactor: 5 surface 1 5.2 Standard Surface type: concrete roughnessfactor: 2 surface 2 5.2.1 Concrete # of concrete sections: 2 5.2.1.1Concrete end 1 coordinate: <−115, 5> end 2 coordinate: <60,5> section 1modal line spacing: 10 width: 10 detected lines: <empty> 5.2.1.2Concrete end 1 coordinate: <−115,−78> end 2 coordinate: <90,−78 >section 2 modal line spacing: 6 width: 6 detected lines: <empty> 6Precision fix # of precision fix points: 1 points 6.1 Precision fixCoordinates: < > Precision fix type: Bluetooth point1 beacon, iBeaconprotocol Beacon MAC address: a:b:c:d:e:f 7 User Policy: standardLanguage: English warning configuration 7.1 Approach WarningDistance: 10LED flash pattern: 1 warning Voice string: <reference to audio Volumeprofile: 85 dBA stored in Smart Positioning System> 7.2 LockWarningDistance: 3 LED flash pattern: 2 warning Voice string: <referenceto audio Volume profile: 90 dBA stored in Smart Positioning System> 8Time of Standard calendar: Holiday list: 12/25 Day open 0600-2200MTuWThFSa, Dependent 0900-2000 Su/Holiday behavior 8.1 Closed Onlyinbound motion during Outbound motion tolerance: 6 hours closed hoursbehavior

In an installation, it may be possible for the site configuration tochange over time during normal operation. For example, a change in theparking lot arrangement could result in a change to the containmentvertices. The site controller can propagate changes by, e.g., updatingthe “Configuration version” field of the system broadcast. A cart, e.g.,the cart's smart positioning system and/or the smart locking wheel—canbe updated wirelessly, via near field communication (NFC), or from adownload from a flash memory card, etc. The site configuration file orground plan 1400 can be stored in non-transitory memory 325 by the smartpositioning system.

c. Example Shopping Cart Modes

A shopping cart within an example system can be in one of several modesat any given time. Major operational modes include but are not limitedto: (1) outdoor, navigating (standard surface, e.g. asphalt); (2)outdoor, navigating (concrete, tile, or other special surfaces withperiodic features); (3) indoor, not navigating; (4) indoor, navigating;(5) outdoor, locked, detecting return direction; and/or (6) beingretrieved by a powered shopping cart retriever such as the CartManagerXD available from Gatekeeper Systems (Irvine, Calif.).

In addition to the operational modes, there can be multiple offline ormaintenance modes, e.g., for firmware updates. In some embodiments, thedead reckoning system can be configured to dynamically change modes ofdead reckoning calculation, e.g., if the vibration signature remainsrelatively unchanged and indicates that the cart is traveling over arelatively smooth surface (e.g., indoors), the dead reckoning system mayassume the cart speed is roughly constant until the vibration signaturechanges substantially to indicate that the cart is changing speed ormoving over a substantially rougher surface (e.g., an asphalt parkinglot). The change in the vibration signature can be detected via anincrease in vibration sensor signals (e.g., in “g”s), an increase invibration power in a vibration power spectrum (e.g., PSD), etc.

d. Exit Detection and Exit Identity Discrimination

A shopping cart can be expected to traverse through an entrance and/oran exit of a retail store. In some embodiments, entrances and exits canbe interchangeable, e.g., a store customer can push a cart into thestore or push a cart out of the store through the same physical opening.In other embodiments, dedicated entrances (only permitting entrance) orexits (only permitting exit) can be used.

For stores with a single exit, it is sufficient to detect that the cartis passing through an exit, which in that case is the only exit. Forstores with multiple exits, the exit detection approach can identifywhich specific exit the cart is passing through. The function ofdetermining which exit a cart is passing through may be called exitidentity discrimination. An embodiment can support exit identitydiscrimination if its positioning uncertainty is less than the minimumdistance between each exit and the centroid of other exits.

The present disclosure provides several different ways of discriminatingbetween exits. Methods of providing both detection and discriminationwith a single feature include:

A beacon, preferably of controlled and relatively narrow beamwidth,either RF (e.g. 2.4 GHz) or ultrasonic, placed near the exit in such away that a cart can be determined to be in the beam versus not in thebeam to a spatial accuracy compatible with the overall required systemaccuracy (e.g., within a few yards or meters accuracy), where the beaconbroadcast encodes the specific exit's identity. Directional antennassuch as the embodiments described in the incorporated-by-reference U.S.Pat. No. 8,558,698 can also be used. Beacons may but need not beBluetooth Low Energy (BLE) beacons implementing a beacon protocol suchas iBeacon from Apple Computer (Cupertino, Calif.) or Eddystone fromGoogle (Mountain View, Calif.).

A magnetic structure in the floor, for example, the magnetically codedfloor mats described in the incorporated-by-reference U.S. Pat. No.8,046,160 (see, e.g., FIGS. 9 and 10 and the relevant specificationtext).

A VLF field where the VLF field is modulated with a unique code whichidentifies the specific exit. The VLF codes can be similar to thosedescribed in the incorporated-by-reference U.S. Pat. No. 6,127,927.

It may be advantageous to separate the precision detection function fromthe discrimination function. For example, in an embodiment whichincorporates a low cost method to determine with high spatial accuracythat the cart is passing through an exit but not which exit the cart ispassing through, the total cost of implementation may be lowered byimplementing the discrimination function separately.

e. Entrance Detection

In some embodiments, the navigation process may not be used indoors,e.g., inside a retail store. In some such embodiments, entrancedetection terminates the dead reckoning navigation process (until thecart exits the store again). It may not be necessary to determine anentrance event to particularly high spatial accuracy.

An entrance can be detected by using the same features as listed in thesection immediately above in combination with a compass/magnetometer.For example, the detection of one of the markers of an entrance/exitalong with the heading is sufficient if all the entrances and exits arealong the same face of the store.

f. Resetting Accumulated Dead Reckoning Errors

Errors can accumulate in dead reckoning systems. Some embodiments canuse an external reference (whose position is accurately known) toprovide a reference position to a cart's dead reckoning system. The deadreckoning system can use the reference position as a new startingposition for subsequent dead reckoning determinations. This can reduceor eliminate dead reckoning errors that were previously accumulated. Anyof the beacons, directional antennas, magnetic structures, or VLF fieldsdescribed herein for entrance/exit detection or discrimination can beused to provide the reference position to the cart.

g. Example Smart Positioning System Implementation

FIG. 15A shows a block diagram 1500 of an embodiment of the smartpositioning system for the shopping cart application. Themicrocontroller 1530 can provide processing functions for the system.The microcontroller can have access to nonvolatile and/or volatilememories. The optional GNSS receiver can provide a GNSS location fix tothe system, e.g., to the microcontroller 1530. Alternatively oradditionally, an optional EAS field detector 1515 can provide an EASlocation fix to the system. A GNSS and/or EAS location fix, whenavailable, can be used to reset the location to the precise GNSS and/orEAS fix and can be used to clear out any accumulated estimation errorthrough dead reckoning. An installation can use the optional GNSSreceiver when the system is outdoors, e.g., in unobstructed view of GNSSsatellites, and use the optional EAS field detector when the system isindoors, e.g., where EAS transmitters are located. Another installationmay have EAS transmitters located indoors as well as outdoors and canuse the optional EAS field detector both indoors and outdoors. Yetanother installation may have indoors GNSS pseudolites and can use theoptional GNSS field detector both indoors and outdoors.

The accelerometer/magnetometer 1510 can provide data used in headingestimation. The accelerometer/magnetometer can output a wake-up signalto the microcontroller. The wake-up signal can be activated to bring themicrocontroller into an active state when the accelerometer/magnetometerdetects motion. Advantageously, the microcontroller can stay in aninteractive, low-power state in the absence of an activated wake-upsignal, thereby reducing power consumption of the system.

The optional ultrasonic coupler 1520 and vibration sensor 1535 canprovide wheel rotation information to the system. This is describedbelow in the section titled Enhanced Rotation Indicating Wheel.

The transceiver 1525 can provide communication functions via BluetoothLow Energy. System information such as site configuration file can becommunicated to the system via the transceiver. The transceiver can alsoprovide location fix through reception of signals generated by a sourceat a known, fixed location. The transceiver can also be used forfeatures such as location-based advertising.

The user notification interface 1540 can provide information, messages,and/or warnings, etc. to a user of the smart positioning system. A usernotification interface 1540 can comprise audio components such as abuzzer, an acoustic resonator (e.g., a sound-producing instrument),etc., and/or visual components such as an LED display, an LCD display,etc.

The power supply component can comprise a primary battery, e.g., aCR123A lithium battery, and a DC/DC power converter, e.g., TI TPS62740.Using the battery as input, the DC/DC power converter can output aplurality of DC supply voltages needed by the various components of thesystem.

Table 2 shows a mapping of the functions in the abstract architecture ofFIG. 4 to specific hardware realizations in the example embodiment inFIG. 15A:

TABLE 2 Example Abstract Function to Realization Mapping AbstractFunction Realization Explanation/Notes Processor + Microchip TheATSAMG55 is a suitable single chip microcontroller memory 425 ATSAMS70for this application. In particular, it is extremely power 300 MHzefficient for computation, provides hardware floating ARM Cortex pointand a DSP instruction set, both of which are M7 1530 or convenient forimplementing many of the required Microchip algorithms, and contains apower-efficient high-speed ATSAMG55 ADC which is convenient forcapturing data from the 1530 vibration sensor(s). heading sensor KionixThe FXOS8700CQ includes both a three-axis 405 and KMX62 or magnetometerand a three-axis MEMS accelerometer, accelerometer 410 Freescale alongwith some built-in processing elements. In and motion FXOS8700CQparticular, the FXOS8700CQ provides a very low power detection sensor1510 motion detection capability, whereby the FXOS8700CQ 450 interruptsthe processor to bring it out of sleep after a programmable accelerationthreshold is achieved, e.g., from someone pushing the cart. SeeFXOS8700CQ data sheet section 7.4 and Freescale app note AN4074.vibration sensor discrete 415 implementation 1535 + 1520 preciseposition/ NXP KW31Z Precise location index received via 2.4 GHz messagedead reckoning 1525; optional from wheel or via localized 2.4 GHztransmitter (e.g., reset interface 435 GNSS receiver either received viatransceiver 1525 or EAS field 1505 and/or detected by EAS field detector1515). EAS field detector 1515 user notification LED plus A series ofLEDs flash to indicate that the cart's wheel is interface 440 speakerplus about to lock. A small loudspeaker can be used to optionalbroadcast voice messages in the standard language(s) of buzzer 1540 thelocale where the cart containment system is located. Optionally, abuzzer such as a piezoelectric resonator is usable to draw the shopper'sattention to the LED. configuration/ NXP KW31Z status interface 1525 445Battery plus CR123 power supply 430 LiMnO2 batteries plus DC/DCconverter, e.g., TI TPS62740 1545

A low-cost, high-sample rate, low-power consumption vibration sensorcould be constructed out of a MEMS process similar to that used incommodity low bandwidth MEMS accelerometers. A suitable example of anaccelerometer with a high sample rate is the Kionix KX123 accelerometer(available from Kionix, Ithaca, N.Y.) with 25.6 kilo samples per second(ksps) per axis. In some embodiments, the vibration sensor and theaccelerometer are the same device. Such embodiments can filter theoutput of the device to obtain vibration data and acceleration data. Forexample, vibration data may be obtained by high pass filtering theoutput; acceleration data may be obtained by low pass filtering(including the DC component) the output.

FIG. 15B shows a block diagram 1550 of another embodiment of the smartpositioning system for the shopping cart application. In thisembodiment, all the components are the same as the embodiment shown inFIG. 15A and are designated with the same reference numerals. Thecomponents are connected differently than the embodiment shown in FIG.15A, however. In particular, the accelerometer/magnetometer 1510 and theoptional EAS field detector 1515 are connected to a secondary processorin the 2.4 GHz transceiver 1525. The accelerometer/magnetometer 1510 canhave an additional motion detect wake-up output connected to thesecondary processor. The secondary processor (e.g., KW31Z) can wake upperiodically to monitor events such as wheel rotation, EAS fieldreception, etc. If an event is detected, the secondary processor canwake up the primary processor to perform its functions. Advantageously,this embodiment can have lower power consumption because of a lowerpower consumption of the secondary processor compare with the primaryprocessor, e.g., microcontroller 1530.

h. Example Shopping Cart Implementation

1. Smart Positioning System Mounting

FIG. 16 shows an example of a cart 1600 including a smart positioningsystem 1605 with a display presenting a notification that the wheel isabout to lock. It can be advantageous to mount the smart positioningsystem to the handle 1610 of the shopping cart, e.g., as shown in FIG.16 (e.g., near the center of the handle). Advantages include: (1)viewing angle(s) of the visible part of the user warning interface canbe convenient to a wide range of user heights; (2) relativelyunobstructed antenna paths for the 2.4 GHz transceiver and optional GNSSreceiver; (3) the handle mounted location can be more protected fromshocks during events such as mechanized cart retrieval than otherlocations on the cart.

FIG. 17 shows a side view 1700 of an embodiment of a smart positioningsystem 1605. The stripe 1705 shows the orientation of the plane of thePCBA (the PCBA itself is inside the enclosure). The semicircularstructure with a protrusion 1710 is the mounting mechanism for placingthe smart positioning system on the handle of a shopping cart. Whenmounted, the handle of a shopping cart be placed in the hollow circularportion near the center of the system. The protrusion is a locking clipwhich can secure the system to the handle.

2. Example Locking Wheel

In some embodiments, a rear wheel may be a smart locking wheel insteadof or in addition to the castered front wheel. In some embodiments, bothfront and rear wheels are castered, which is described below in sectiontitled Front and Rear Castered Wheels. An example of a smart lockingwheel that can be used with a shopping cart is the SmartWheel® 2.0QSwheel available from Gatekeeper Systems, Inc. (Irvine, Calif.).

Referring back to FIG. 3, an example smart locking wheel 215 can haveone or more of the following capabilities and properties: (1) ability tocommunicate with the smart positioning system using wired or wirelesslinks 365, e.g. via a 2.4 GHz RF link; (2) ability to lock and unlock380 in response to commands sent from the smart positioning system. Insome implementations, “lock” includes locking the wheel to preventrotation and inhibiting rotation of the wheel about its axis. Forexample, rather than being rigidly locked, a locked wheel may besubstantially more difficult to rotate than in an unlocked (e.g.,freewheeling) state. A locked or locking wheel can include a wheel witha brake that can inhibit or prevent rotation of the wheel about thewheel's rotation axis; (3) ability to detect and timestamp rotation ofthe wheel 375; (4) ability to detect motion or the absence of motion, sothat the wheel may enter a low power “sleep” state when the cart is notmoving; (5) ability to detect and decode very low frequency 360 (VLF,typically extending from 3 kHz to 30 kHz, e.g., 8 kHz) fields such asthose described in U.S. Pat. No. 6,127,927. Detection of the VLF fieldscan be used by the smart positioning system to actuate the wheel'slocking mechanism (e.g., when the wheel moves past a containmentboundary) to prevent theft of the shopping cart if the VLF field'sradiating cable is located at a boundary of cart containment, or also asan anti-shoplifting measure such as implemented by the Purchek® systemavailable from Gatekeeper Systems; (6) ability to detect magneticmarkers 360 such as the magnetic markers described in U.S. Pat. No.8,046,160 (see, e.g., FIGS. 6 through 10 and the relevant specificationtext). Specific locking wheel implementations may not provide all ofthese capabilities or may provide additional or different capabilities.

3. Wheel/Caster Configurations

In some embodiments, a locking wheel can be mounted in the front, e.g.,castered, position. In some embodiments, a first locking wheel can bemounted in the front position, and a second locking wheel can be mountedin the rear position. Although it may be considered undesirable to haveone or more locking wheels only in the rear because it may be mucheasier to continue to push a cart with a locked wheel only in the rear,some embodiments can be configured with a locking wheel mounted in therear position. Section titled Front and Rear Castered Wheels describesembodiments in which all four wheels of a cart are castered.

An embodiment according to the present disclosure may have one of atleast four different configurations of wheels and casters on the cart:

One, the cart has a noncastered rear wheels. At least one of the rearwheel can be a smart wheel capable of rotation detection andcomputation/logic processing. A castered front wheel can be equippedwith a locking mechanism. Having locking front wheels can beadvantageous because it may be easy to push a cart with only a rearwheel locked; cart containment may be less achievable as a result. Thisconfiguration is the default configuration for this disclosure. However,the disclosure is not limited to this configuration.

An installation which requires position tracking capability but not cartcontainment functionality through wheel locking, (e.g., tracking themotion of the cart only, or using only audio/visual warnings from thedead reckoning system) can have nonlocking front wheels, e.g., wheelswithout electronics and/or a locking mechanism.

In a second configuration, the smart locking wheel can be a front wheel.The smart wheel can perform all the functionalities described in thisdisclosure, e.g., rotation counting, wheel-related detection, andlocking and unlocking.

In a third configuration, all four wheels are castered (e.g., as can becommon in Europe). Thus the cart can “crab”—not go straight forward orbackward. In this configuration, both a front and a rear wheel can havethe various detection functionalities. In this configuration, the roleof master wheel can change between the front and rear with respect tostate transition diagram 560. An embodiment may use a rear smart wheelas a default master wheel and switched to a front smart wheel as themaster wheel as needed, for example, when the cart is consistently goingbackward, e.g. being pulled by the handle rather than pushed. Seesection below titled Front and Rear Castered Wheels for additionaldescriptions.

In a fourth configuration, a rear wheel signals rotations to the smartpositioning system without having any intelligence in the rear wheel,e.g. via the ultrasonic tuning fork in the wheel being struck. Thisconfiguration is described immediately below.

4. Enhanced Rotation Indicating Wheel

One embodiment of the wheel uses a tuning fork as a method of conveyingrotation information to the dead reckoning system. A tuning fork and astriker can be placed in a wheel to produce a strike of the tuning forkfor each rotation of the wheel. For example, a tuning fork may be placedin a stationary part of the wheel, e.g., attached to a wheel axis. Astriker may be placed in a rotating part of the wheel. In someembodiments, the placement may be reversed, e.g., the tuning fork isrotating and the striker is stationary. Such an enhanced rotationindicating wheel can detect wheel rotation without requiring electricalenergy in the wheel. This can be achieved, for example, through anultrasonic sensor dead reckoning system. An ultrasonic sensor deadreckoning system can detect the ultrasonic pulses associated withrotations of a wheel which cause a striking of the tuning fork. Theultrasonic energy can propagate from the wheel either through the air orthrough the structure of the wheeled object to the ultrasonic sensor.

The resonant frequency of a tuning fork is given by Equation (1):

$\begin{matrix}{{f = {\frac{1.875^{2}}{2{\pi \cdot l^{2}}}\sqrt{\frac{E \cdot I}{\rho \cdot A}}}},} & (1)\end{matrix}$where f is the resonant frequency, l is the length of the tines, E isYoung's modulus of the material, I is the second moment of area of thetines, ρ is the density of the material, and A is the cross-sectionalarea of the tines.

For example, a tuning fork made out of 308 stainless steel, withrectangular tines having a width of 1.1 mm and a length of 5 mm, has aresonant frequency of 22 kHz, above the range of human hearing.

One or more wheels of a wheeled object can be a wheel with a tuningfork. A wheel with a tuning fork and a striker can have low componentcost and low energy cost (e.g., no electrical power is required togenerate ultrasonic pulses), making multiple enhanced rotationindicating wheel an inexpensive and practical solution. More accuratewheel rotation data can be obtained through the use of more than onesuch wheels. For example, potentially bad data due to poor contactbetween a wheel and the ground can be identified by comparing data fromdifferent wheels. As another example, changing cart heading translatesto more rotations of the front castered wheels than the rear wheels onan axle. Rotation data from both a front wheel and a rear wheel can beused in the estimate of changing heading.

Where more than one wheel has a tuning fork, each tuning fork may have adifferent resonant frequency from differences in their physicalcharacteristics due to manufacturing variation. The resonant frequencyof each wheel can be characterized during cartmanufacturing/installation and stored in memory. Calibration data forresonant frequency across operational temperature range can be measuredduring manufacturing and stored in memory. The dead reckoning system candistinguish the source of an ultrasonic pulse through the resonantfrequency of the pulse, temperature compensated as needed.

In an embodiment, the axle can be rigidly fixed to the caster fork; therotating part of the wheel (e.g., hub and cover) can rotate around theaxle with a pair of waterproof bearings. In a configuration wherein thetuning fork is rigidly coupled to the axle, the ultrasonic energy fromthe tuning fork can be coupled into the entire caster fork. The strikercan be molded into one of the rotating parts, either hub or cover.

For a cart with noncastered rear wheels, the caster fork can be directlywelded to the cart frame. In this embodiment, the ultrasonic energy cancouple through the entire frame of the cart. Depending on details of thecart handle construction (e.g., some cart handles are welded steel tubeswhich are directly mechanically coupled to the rest of the frame; othersare plastic or fiberglass, both of which can be heavily damping atultrasonic frequencies), the ultrasonic energy will either coupledirectly into the smart positioning system or will couple via the air inthe vicinity of the smart positioning system.

For a cart with all castered wheels, the rear caster fork, which is hardcoupled to the tuning fork via the nonrotating axle, can provide arelatively large of area, on the order of 30 to 40 square centimeters,to couple acoustic energy into the air (from which the energy thencouples into the ultrasonic receiver in the smart positioning system).An embodiment can use the rear rather than the front because the shorteracoustic path in the air to the smart positioning system (e.g. on handleunit) can provide stronger signal at the receiver.

5. Example Warning/Locking/Unlocking Behavior

The behavior of the cart (e.g., notifications to the user, and underwhich conditions the wheel locks and unlocks) can be adjusted to meetthe customer's needs. In some embodiments, the behavior as the cartapproaches the containment boundary includes the following: (1) When theestimated position of the cart is within a certain distance of thenearest point of the containment boundary, e.g., the distance beinggiven by the field WarningDistance of the currently active configuration(e.g., see Table 1).

The navigation system can warn the user that a lock event is imminent.There may be multiple warning distances with different notifications tothe user, such as different colors or flashing rates of the LEDs,different duty cycles on the buzzer, etc. (2) As the estimated positionof the cart is crosses the containment boundary, the navigation systemcan command the locking wheel to lock. (3) The wheel can remain lockeduntil it is unlocked, e.g., by a store employee using, for example, ahandheld device which generates a specific wireless command (e.g., an RF2.4 GHz command) to the wheel.

In some embodiments, the wheel may be unlocked when the cart has beenpushed or dragged a certain distance back away from the containmentboundary (e.g., back toward the store). Since the wheel is locked, thevibration spectrum of the cart may be different from the case where thewheel is rolling on the same surface. The vibration spectrum can beanalyzed before or during installation. The site configuration file caninclude additional parameters to support this usage mode.

To protect against someone trying to steal the cart by dragging itbackward (further away from the containment line), a system whichrequires the behavior of unlocking when being pushed or dragged backinward can include a castered wheel containing a magnetometer/compass,and use the magnetometer/compass in the wheel rather than themagnetometer/compass in the dead reckoning system as the heading sourceduring a locked state. A magnetometer located on the cart handle may notindicate two different headings depending on whether the cart is movingforward or backward. On the other hand, a magnetometer located on acastered wheel can indicate different headings when the cart is movingbackward rather than forward, since the castered wheel turns accordingto the cart's direction of movement.

i. Example Installation and Calibration

An example site configuration file, e.g., as shown in Table 1, can becreated through an installation design process. The installation designprocess can take place offline, using tools such as a custom applicationusing a map provider's application programming interface (API) (e.g.,Google Maps API) to identify the spatial features of interest (e.g.exits, entrances, containment vertices, concrete sections, etc.). Duringthe installation design process, the relative coordinates of thesefeatures can be obtained from the overhead imagery. Information obtainedmay be cross-referenced and verified with the customer's orders. Duringsite installation process, information obtained during the designprocess may be confirmed through actual observation at the site.

Some embodiments of the system can allow for installation of smartwheels and smart positioning systems onto existing shopping carts in thefield. The physical installation of the smart wheel onto the cart iswell understood (for example, the existing Gatekeeper SystemsSmartWheel® 2.0QS). The smart positioning system mounting can depend onthe implementation of the cart handle. For handles that are part of thecart's rigid frame, the smart positioning system can include amagnetometer and an accelerometer, for example, on a printed circuitboard assembly (PCBA). Various calibration procedures can be performedas described below.

1. Example Off-Line Calibration

In some embodiments, the dead reckoning system can include a mechanismby which a service technician can initiate a service/maintenance mode,of which calibration can be a submode.

One example method of triggering service/maintenance mode is to hold apermanent magnet next to the dead reckoning system in a specificorientation. The DC magnetic field can be detected by the magnetometer,and the dead reckoning system can interpret a field of the appropriatestrength and orientation as a command to enter service mode.

Once service is initiated, the dead reckoning system can communicate viaBluetooth Low Energy with a handheld device such as a smartphone ortablet (e.g., iOS or Android devices). The handheld device can containapplication software to assist the installation technician in thecalibration process.

To enable communication to the individual units, the wheel and the deadreckoning system can have unique media access control (MAC) addresses ontheir RF (e.g., 2.4 GHz) links.

It may be advantageous to orient the accelerometer's 3 axes to thecart's body frame. An example of the cart's rigid body coordinate systemis indicated in system 230 of FIG. 2: x forward, y left, z up. Throughthe calibration application on the handheld device, the installationtechnician can orient the accelerometer at any time that the cart ishorizontal. Given the knowledge that the cart is horizontal, theorientation of the accelerometer in the xz plane can be determined fromhow the gravitational field resolves into the accelerometer's x and zaxes. Orientation of the accelerometer relative to the cart body in thexy plane, if needed due to displacement of the cart handle from the yaxis, can be performed by pushing (accelerating) the cart in a straightline.

The orientation of the magnetometer with respect to the accelerometercan be fixed at the time of manufacture of the dead reckoning systemPCBA(s). Calibration of the offset and gain of the three magnetometeraxes can be performed as part of dead reckoning system manufacturingprocess, e.g., by applying a series of known magnetic fields to themagnetometer via Helmholtz or Maxwell coils. The response of themagnetometer to the known, applied magnetic fields can be used togenerate a calibration model usable to translate raw magnetometerreadings into magnetic fields.

The magnetometer may often require hard and/or soft iron calibration,particularly if the cart handle material is ferromagnetic, e.g., mildsteel or if the cart has an adjustable child seat and the magnetometeris disposed in or on the handle of the cart. A sufficiently accuratehard and soft iron calibration for some purposes can be performed by theservice technician spinning the cart around the z axis only (1, 2, 3 ormore spins can be used): while not fully accurate, as long as theshopping cart is constrained to a surface that is near level, as isusually the case, a post-correction heading accuracy on the order of twoto five degrees can be obtained using this method.

As described above in the section titled Reducing Error in HeadingEstimation, tilt of the ground surface can affect the accuracy of themagnetometer. At locations where the vertical component of geomagneticfield is about twice its horizontal component, e.g., in North Americaand Europe, achieving a heading estimate accuracy of one degree mayrequire correcting for surface tilt (deviation from horizontal) of morethan two degrees. At locations with a different geomagnetic fieldprofile, correcting for a different severity of tilt may be required.

An embodiment may have a design target of 1 degree heading accuracy tosupport a site with a length of several hundred feet. A lower headingaccuracy may be sufficient for a small site, e.g., a strip mall. Forheading accuracies of better than one degree, a more accurate hard andsoft iron compensation can be performed. The method can be performed,for example, by applying a series of known magnetic fields to themagnetometer, while the dead reckoning system is attached to the handleof the cart, via Helmholtz or Maxwell coils. The response of themagnetometer to the known, applied magnetic fields can be used togenerate a calibration model usable to translate raw magnetometerreadings into magnetic fields. Because the dead reckoning system isattached to the cart handle during the calibration procedure, thiscalibration method can compensate for the ferromagnetic material in thecart handle.

6. Example Temperature Compensation of Magnetometer

A dead reckoning system operating in a retail store setting mayexperience a wide range of temperatures, e.g., from severe winter to hotsummer weather in the long term, and from climate controlled storeinterior to exterior whether elements in the short term. A magnetometermay be temperature sensitive and can require compensation acrossoperating temperature range. Such compensation can help the deadreckoning system achieve the required accuracy across the operatingtemperature range. Units of magnetometers may need to be calibratedindividually. This can be done during manufacturing e.g., after PCBA(for example, after the reflow process which can alter the temperatureprofile of a magnetometer). Magnetometer data can be measured at threeor more temperature points. The calibration data can be stored inmemory. In operation, a temperature sensor in the dead reckoning system(e.g., physically close to the magnetometer, for example, on or near themagnetometer die, or within a distance of 1 cm to 5 cm of themagnetometer) can sense operational temperature. The processor cancompute a temperature compensation factor through, for example,polynomial interpolation of the calibration data based on the measuredtemperature. The processor can compensate for the temperaturesensitivity of the magnetometer using this computed factor.

To provide a specific example, at the factory, each individualmagnetometer can be calibrated (per axis) for offset and gain at amagnetic field value on the order of ±50 μT at multiple temperatures.The number of temperatures at which the calibration is needed can dependon how accurate the temperature calibration needs to be, and on hownonlinear the gain and offset versus temperature curves are for theparticular embodiment of magnetometer. For example, for the KMX62 in ashopping cart application, a residual error after temperaturecompensation of 0.1 μT over an operating temperature range of 15° C. to50° C. can be a calibration target. The minimum output noise level ofthe KMX62's magnetometers in the lowest noise mode is about 0.2 μT.Hence a calibration target of 0.1 μT is reasonable in light of theinherent noise of the sensor. Measuring the gain and offset of each axisat three temperatures (e.g. −15° C., 25° C., and 50° C.) during factorycalibration and linearly interpolating the results can produce RSSerrors on the order of 10 nT.

VI. Example Applications

a. Technical Challenges

The following implementation constraints can be applicable to theshopping cart containment problem, and in some cases may make otherwisepractical solutions challenging or impractical to implement. Some ofthese constraints may also apply in other contexts or applications.

It may be advantageous for a shopping cart locking wheel to have thewheel's battery sealed inside the wheel at the time of manufacture. As aresult, the battery may not be replaceable. In contrast, a handlemounted dead reckoning system can be designed to support replaceablebatteries (see example in FIG. 17).

Some embodiments may include wheels containing an energy harvestingsystem, such as that described in U.S. Pat. No. 8,820,447. In suchembodiments, the energy asymmetry between the smart positioning systemand the smart locking wheel can be reversed (e.g., the smart positioningsystem becomes more energy constrained then the wheel). Energy in thesmart positioning system becomes the quantity to conserve. In suchembodiments, the main processing function can be migrated from the smartpositioning system to the smart locking wheel, and the smart positioningsystem can accumulate heading and attitude information to relay to thesmart locking wheel for processing.

b. Front and Rear Castered Wheels

In some embodiments, all four wheels of the wheeled object are castered.In such embodiments, the constraint that the path taken by the cart'sbody-centered velocity vector points “forward,” e.g., normal to the linebetween two corresponding caster axes, may not apply.

FIG. 18 illustrates this phenomenon. In plot 1800, a shopping cart 1805is moving in the forward direction, e.g., perpendicular to the wheelaxles of the cart. The four wheels 1815 are aligned in the direction ofcart motion, which is parallel to the x-axis. The magnetometer insidethe smart positioning system 1810 produces a heading based on the cart'sorientation, e.g., the x-axis.

In plot 1830, the shopping cart 1805 is turning clockwise. The wheels1815 are aligned according to the direction of motion at each individualwheel. However, the four wheels may not be aligned with each otherbecause the front of the cart and the rear of the cart are not turningin an identical direction. The magnetometer inside the dead reckoningsystem 1810 produces a heading based on the cart's orientation, e.g.,the x-axis at the start of the turn, and the y-axis at the end of a 90°turn. The magnetometer can produce correct heading data in spite of theturn.

In plot 1860, the shopping cart 1805 is crabbing, e.g., moving sideways,parallel to the y-axis. The four wheels 1815 swivel to align in thedirection of cart motion, parallel to the y-axis. But the magnetometerinside the dead reckoning system 1810 detects no change in the headingof the cart. The magnetometer output may be essentially the same as theoutput in plot 1800. Dead reckoning based on the magnetometer output canproduce a position estimate which is erroneous. Similar error can occurwith four castered wheels in all directions except the forwarddirection, as illustrated in plot 1890.

One solution to the absence of this constraint is to include amagnetometer in at least one wheel, e.g., heading/caster angle detector383. The dead reckoning system can combine readings from themagnetometer in the wheel with readings from the magnetometer in thesmart positioning system to estimate the cart's heading. For example,crabbing motion (e.g., as illustrated in plot 1860 or 1890) may bedetected when readings from the two magnetometers have a largedifference, and is not followed by a subsequent change in headingestimate from the magnetometer in the smart positioning system. For suchmotions, the system can use data from magnetometer in the wheel and notdata from magnetometer in the smart positioning system. As anotherexample, turning motion (e.g., as illustrated in plot 1830) may bedetected when readings from the two magnetometers have a largedifference, and is followed by a subsequent change in heading estimatefrom the magnetometer in the smart positioning system. Distinguishingturning motion from other types of motions, e.g., crabbing motion, withonly a magnetometer in one wheel in addition to a magnetometer in thesmart positioning system may be computationally expensive, however.

Another solution to the absence of the constraint on cart motion inassociation with front and rear castered wheels is to include amagnetometer in at least one front and one rear wheel. The heading ofthe cart body can be estimated as, for example, approximately theaverage of the headings of the front and rear wheels. In such anembodiment, the wheels can store at least raw magnetometer readingsalong with the timestamped rotation detections; these raw magnetometerreadings can be processed together with the smart positioning systemmagnetometer and accelerometer time series data to yield the carts'heading history. With a magnetometer in at least one front wheel and onerear wheel, the system can distinguish turning motion from crabbingmotion by comparing magnetometer readings from a front wheel versusconcurrent readings from a rear wheel.

An additional or alternative solution is to provide a sensor by whichthe wheel can directly determine its caster angle, e.g., the anglebetween the wheel's direction of motion and the cart body.

c. Indoor Modes

Indoor dead reckoning can be used for multiple functions, including butnot limited to: (1) tracking shopper behavior (e.g., dwell time andmovement throughout the store), for post-processing analytics, or forreal-time behavior such as sending targeted advertising to a shopper(which may be output on the display of the smart positioning systemattached to the cart handle), estimating that a large number of shoppingcarts are heading for the checkout area (e.g., to increase the number ofcheckout personnel), etc.; (2) using dead reckoning estimates to infershoplifting, for example, travel through (and perhaps pause at) theparts of the store which have high-value, theft-prone items such asliquor or cosmetics, followed by motion of the cart toward an exitwithout passing through a checkout station. Indoor dead reckoning canadvantageously supply both direction and speed information. Thisenhances the likelihood of correctness of an inference of shoplifting.For example, a cart being rushed as it heads toward an entrance/exitleaving the store is more likely to be involved in shoplifting than acart being rushed as it heads toward an entrance/exit entering thestore. As another example, a cart passing a checkout stand slowly (e.g.,and stopping) is less likely to be involved in shoplifting than cartpassing a checkout stand quickly (e.g., without stopping).

An implementation of merchandise loss prevention based on dead reckoningcan be based on user or cart behavior derived from dead reckoningestimates. For such applications, position tracking using a deadreckoning system can replace position tracking using, e.g., two-waycommunications, such as disclosed in U.S. Pat. No. 8,570,171 (System forDetecting Unauthorized Store Exit Events Using Signals Detected byShopping Cart Wheels Units). Advantageously, position tracking using adead reckoning system may not require signal sources at fixed locations,e.g., electronic article surveillance towers, access points, etc.,thereby reducing infrastructure cost of the surveillance system. U.S.Pat. No. 8,570,171 is hereby incorporated by reference herein in itsentirety for all it discloses.

Relative to an embodiment for outdoor applications, an embodimentadapted to perform these example indoor functions may include one orboth of the following modifications: (1) Modification of the transferfunction from magnetometer readings to georeferenced heading. (2) Arotation estimation algorithm optimized for use on tile or linoleumfloors, which are significantly smoother than asphalt.

The magnetic field inside buildings (e.g., retail stores) can besignificantly distorted from the geomagnetic field at the building'slocation. The distortion may primarily be caused by inducedmagnetization in the building's ferromagnetic elements (e.g. structuralsteel). An embodiment can add a single, constant correction vector toall magnetic field vectors measured within the building to correct forthe distorted magnetic field. The correction vector can be a spatialaverage of the difference between the actual magnetic field measured atvarious points inside the store and the geomagnetic field at the store'slocation. The averaging can take place over an ensemble of locationswhich correspond to locations within the store that carts may beexpected to traverse.

Some embodiments may implement a correction scheme involving storing amap of the magnetic field correction vectors, e.g., in a sparse gridcorresponding to the individual points of the ensemble mentioned in theprevious paragraph. The navigation algorithm, e.g., running on the deadreckoning system, can interpolate the instantaneous correction vectorbased on the present dead reckoned position. The correction vector(s)can be stored in the memory of the dead reckoning system (e.g., aslookup tables).

At a site where the ground has regularly spaced joints, e.g., tiles,dead reckoning algorithm can use vibration analysis to detect a cartcrossing a tile joint. The distance traveled between joint crossings cansimply be the size of a tile. Heading estimate can provide adjustmentneeded in the distance estimate when a cart does not travel in astraight line and does not cross tile joints at right angles. Tile sizecan be stored as parameters in the site configuration file.

The basic idea of detecting and counting expansion joint lines inconcrete can be adapted to counting tile crossings indoors. The ambientvibration level can be far less indoors (due to the smoother surfaces ofindoor floors compared to outdoor surfaces), and the coupled impulsefrom the tile joint can be much lower in amplitude than concreteexpansion joints.

Specifically, an embodiment for tracking position of indoor shoppingcarts can function as described below:

Upon entering a store, e.g., passing through store exit 126 in FIG. 1 or1415 in FIG. 14 toward the store interior, a cart equipped with a deadreckoning system may begin indoor tracking using the entrance (exit)location as the initial position for dead reckoning. This location mayor may not be augmented by specific precision fix (e.g., magneticsignature) readings at known points inside the store. Also upon enteringthe store, the cart may receive a start indoor navigation signal. Thisstart indoor navigation signal may also provide operational parametersto the cart. The operational parameter information can be used toidentify key locations inside the store and zones associated withtriggering an anti-theft logic. For example, as the cart enters thestore, it can be given the coordinates for checkout lanes and/or paypoints in the store. It may also be given coordinates for where totrigger the anti-theft logic. With this information in the system, if orwhen the cart crosses the boundary of one of the anti-theft zones, thesystem can be triggered to prevent the cart from leaving the storewithout visiting a pay point or a checkout register.

While indoor, the cart can identify, through dead reckoning, if itpasses through a register lane or is at a location in the store wherepayment transactions take place. For example, by combining the locationof the cart and utilizing motion information such as heading and speed,an embodiment can determine whether the cart is in the vicinity of aregister lane or a pay point and exhibits the motion profile associatedwith a shopper who is paying for merchandise. If so, the system canregister that the cart is authorized to exit the store (e.g., by settingthe state of the exit authorization to an authorized state), not lockingthe wheel and/or triggering alarms on the way out of the store. Afterthe cart exits the building, the system can terminate indoor navigationmode, clear the state of the exit authorization, and begin outdoornavigation if triggered to do so.

If, on the other hand, the cart does not satisfy the criteria ofpurchasing merchandise at any time it is inside the store and attemptsto exit the store, the system can determine via dead reckoning logicthat the cart is attempting to exit but has no authorization to leavethe store. The system can lock the wheel and/or trigger alarms. Thealarms may be on the cart and/or external to the cart, e.g., on anelectronic article surveillance tower which can communicate with thesmart positioning system. Triggering the anti-theft system can be donein connection with high-value and/or high-risk merchandise areas such asliquor, health and beauty, etc. Alternatively or additionally,triggering the anti-theft system can be done based on the cart passing aboundary line, e.g., near an exit of the store.

In order to augment the accuracy of the dead reckoning algorithm, anembodiment can compare the actual magnetic field it reads to apreviously recorded magnetic field mapping for the store. Key points inthe store can be surveyed during the system installation phase; magneticsignatures for these key points may be stored in a table. When a systemdetects via dead reckoning navigation that it is near one of thesesignature points, it can compare its actual reading to the storedreading and can determine when it is actually in the vicinity of thestored magnetic field reading point. This can be used to reset errors inthe dead reckoning algorithm.

d. Position Estimation Via Radius Fix or Hyperbolic Fix

In lieu of or in addition to dead reckoning, an embodiment may performposition estimation through radius fix using RF signals. For example, asingle cooperating RF beacon/locating point, e.g., 395 in FIG. 3, can belocated at a location known to the navigation system. Either the RFbeacon or the navigation system can serve as the transmitter for theradius fix; the other device is the receiver.

In an installation where both the transmitter and receiver are capableof changing frequency without changing the phase of the phase lockedloop (PLL) underlying the respective frequency synthesizers (RF chipswith such capability include the NXP MKW31Z and the MicrochipAT86RF215), the transmitter can transmit at several differentfrequencies. The phase difference of the path can be estimated from thereceived signals. This phase difference may be computed as radius (e.g.,distance between the transmitter and the receiver) modulo wavelength atthat particular frequency. With phase differences derived at severalfrequencies, a single value of radius can be computed, e.g., through amodular arithmetic approach finding the value of radius which can matchall the different measured phase values. In practice, with noise andother issues, the modular arithmetic approach can used in conjunctionwith a best fit estimator.

In an installation where both RF and ultrasonic transmitter and receiverare available, radius fix can be computed through the use of both RF andultrasonic signals. A fixed unit, e.g., the beacon, can be theultrasonic transmitter. This can be the preferred embodiment becauseultrasonic transmission consumes more power than ultrasonic reception,and because the fixed unit typically can have a line-power source.However, the wheeled object may function as the ultrasonic transmitteras well. Upon request for a radius fix (e.g., from either the wheeledobject or a fixed unit, e.g., initiated by a central processing system),the transmitter can send both an RF transmission and an ultrasonic burstat the same time. The radius may be computed as the difference inreception time divided by speed of sound.

In lieu of or in addition to dead reckoning, an installation may provideposition estimate via hyperbolic fix. Such an installation can have twoantennas (e.g., 900 MHz or 2.4 GHz) on the fixed side, e.g., an RFreceiver at a fixed location. Each of the two antennas can be connectedvia a coaxial cable of known length to an input of an RF phase detector.The RF phase detector can output the phase difference between the twoinputs. A wheeled object with the smart positioning system can transmitsequentially on several different frequencies. This operation can besimilar to the first example above for radius fix, except without therequirement that the transmitter can change frequency without changingphase of underlying PLL. The fixed side can obtain a series of phasedifferences as a function of frequency. Using the same approach asdescribed in the first example for radius fix, a signed differentialdistance can be derived from the phase differences. The signeddifferential distance can define one half of a hyperboloid of twosheets. If the wheeled object is confined to a plane, as in the shoppingcart case, the intersection of the plane and the hyperboloid is ahyperbola. The cart's position can be estimated to be on the hyperbola.The radius fix or the hyperbolic fix can be used in combination withdead reckoning position estimates to improve the accuracy of a positionfix.

VII. Additional Improvements

a. Navigation History and Backtracking

Some indoor navigation and backtracking algorithms can becomputationally intensive. For example, indoor navigation usingbacktracking with particle filters can improve location accuracy byincluding structure floor plans (see, e.g., description with referenceto FIG. 14) as constraints on position estimates. However, the highpower requirements of indoor navigation and backtracking algorithms maybe unsuitable for certain applications that are highly sensitive topower requirements such as a navigation system for a shopping cart.Accordingly, in some embodiments, some portion of thecomputational-intensive navigation calculations can be distributed fromthe navigation system on the cart to a remote computing system (e.g., inthe “cloud”) that performs the calculations and returns results to thecart navigation system. The remote computing system (sometimes referredto as a base station) can be connected to the cart navigation system viawireless techniques (e.g., a LAN, WAN, Bluetooth connection to theInternet, etc.). In some such embodiments, communication between thecart navigation system and the remote computing system (and offloadingthe processing to a base station) can be managed using embodiments oflow-energy consumption techniques described in U.S. Patent PublicationNo. 2016/0259061, Low-Energy Consumption Location of Movable Objects,which is hereby incorporated by reference herein in its entirety.

A smart positioning system 210 (e.g., as described with respect to FIG.2) on a cart can implement a less computationally intensive alternativeto particle filter algorithms. The positioning system may handle some orall of these computations (or, as described above, offload some of thecomputations to a remote base station processing device). The lesscomputationally intensive algorithm can help with navigating a shoppingcart in an indoor environment with many barriers to free movement of thecart (such as shelves in a grocery store). A graph traversal approachcan be implemented, where each node in the graph represents a region inwhich the cart's motion is unconstrained, such as a specific aisle, andthe edges of the graph represent paths connecting the nodes, e.g., thezone at each end of an aisle where the aisle empties into a broaderconnecting area (each broader connecting area being a node as well, withedges to each aisle). Nodes of the graph can be weighted based on e.g.,confidence of the cart's estimated position, and if (as described withreference to FIG. 22) the smart positioning system 210 determines thereis an error in the estimated position, the nodes can be re-weighted andthe estimated position re-calculated (e.g., via backtracking).

An example of a backtracking scenario will be discussed with referenceto FIG. 22, which shows a section of a store with a single set ofparallel aisles, with connecting aisles at each end. Merchandise shelvesare indicated by cross-hatch. The section shown in FIG. 22 could be aportion of the store interior 1410 described with reference to FIG. 14.Additional, similar aisles may exist to the left and right of thoseshown in FIG. 22. For convenience of description, the primary aisles areoriented North-South, although this is for illustration only and is nota limitation. Nodes may be disposed in or along the aisles, and thesenodes may provide to the smart navigation system a position (e.g., thenode's position is assumed to be accurately known) as the cart passesthe node. Examples of nodes include RF beacons 395 or fixed features 385described with reference to FIG. 3. These position “fixes” from thenodes can be used by the navigation system to increase the accuracy ofthe dead reckoned position estimate. Embodiments of the smartpositioning system 210 can store (or communicate to a base station forstorage) a history of prior cart positions, a history of positionestimates received from nodes, or histories of other navigation data(e.g., magnetometer measurements, wheel rotation estimates, etc.) and,as described in the following illustrative backtracking scenario, usethe history data to improve the accuracy of a dead reckoned positionestimate.

In an example backtracking scenario, the cart 205 begins at position 1in FIG. 22. The center of the cart handle is taken as the referencedatum for all positions in this discussion (which is where the smartpositioning system 1605 is commonly located).

The actual cart track is through positions 2, 3, and 4 as shown in FIG.22, ending up in Aisle A. However, in this scenario a severe transienterror in the magnetometer reading causes the estimated dead reckoningpath to diverge, following the dotted track from position 2 to(erroneous) positions 3′ and 4′.

Position 3′ is actually impossible, since the cart cannot occupy thesame volume as the merchandise shelving, so the dead reckoning algorithmwith backtracking will assign a very low confidence to that deadreckoned position. However, at position 3′ the most probable physicalreality according to the dead reckoning algorithm is that the cart hasnot made quite as much forward travel as the dead reckoning indicates,and the actual position is something like 3″, which is in Aisle B butnot inside the shelving. Continued travel to dead reckoned position 4′,going straight through a merchandise shelf, brings the probability lowenough that backtracking is triggered. In this case, the dead reckoningalgorithm reexamines the stored history of sensor measurements goingback to the last confidently known position, 2, and finds the mostprobable node that could be reached from position 2 with reduced orminimum assumptions regarding sensor errors.

In this illustrative scenario, there is assumed to be no reason for thedead reckoning algorithm to doubt the rotation counting from position 2onward (e.g., no changes in implied wheel rotation rate that areincompatible with measured x-axis acceleration), so the algorithm mayassume that there was a heading error of unknown duration and magnitudeat some point after leaving position 2. The node that can be reachedwith the reduced or minimum error assumption on heading is node 4, whichin this scenario is correct, although the dead reckoning algorithm willhave very low confidence in its estimate of the North-South position ofthe cart until another node transition, e.g. a turn onto Node 1 or Node2, allows the North-South error to be bounded.

b. Determining Motion Direction for Various Dual Swivel CastorEmbodiments

Tracking a cart, such as by dead reckoning, can involve determining adirection of motion for the cart. Carts with different castorimplementations can determine the direction of motion in different ways.

Some carts can feature one or more wheels that swivel on casters and oneor more wheels coupled to an axel. For example, two front wheels canswivel on casters while the axles rigidly fix two rear wheels to thecart frame (so that the rear wheels are always pointing parallel to thedirection of the cart, e.g., perpendicular to the handlebar). In such anexample, the cart's instantaneous motion vector is normal to the linebetween the two rear wheels. A directional sensor, such as amagnetometer, can be placed on a variety of positions to determine cartdirection. For example, the magnetometer can be coupled to a rear wheelor anywhere on a cart body (e.g., the handlebar) that is rigidly fixedin direction with respect to the rear wheels.

For carts on which all four wheels have swivel casters (e.g., asdescribed in the section entitled Front and Rear Castered Wheels, it canbe more difficult to determine the angle that the cart is moving. Forexample, as shown and described with reference to FIG. 18, plots 1800,1830, 1860, and 1890 show different directions that a cart with fourswivel casters can move. A magnetometer rigidly mounted to the frame orbody of a cart may not necessarily indicate a direction of motion of thecart. Accordingly, a sensor can be used to determine the directionalheading of a wheel independently of the directional heading of the bodyof the cart. In some embodiments, a magnetometer or other directionalsensor can be positioned in at least one of the swiveling wheels orcasters, and the direction of the wheel can be used to determine thedirection of the cart. In some embodiments, a sensor can be used todetermine the swivel caster angle relative to the body of the cart.

Low cost, low standby power, and shock resistant systems for rotationcounting on cart wheels tend to involve rotating permanent magnetsinside the rotating wheel hub. The rotating permanent magnet activates asensor in a non-rotating chassis such as a reed switch (e.g., anMK22-B-2 from Standex-Meder Electronics (Cincinnati, Ohio)), a Halleffect sensor (e.g., a DRV5023 from Texas Instruments (Dallas, Tex.)),or a magneto-resistive sensor (e.g., an RR120 from Coto Technology(North Kingstown, R.I.)). Such rotating magnets can create disturbancesin the magnetic field detected by the magnetometer and can reduce theaccuracy of a navigation system relying on the magnetometer.

In some embodiments, the magnetometer can be located farther from themoving magnet, reducing the effect of the rotating magnet on themagnetometer. A first wheel, such as a rear smart locking wheel (such assmart locking wheel 215 of FIG. 3) which may or may not be fixed (e.g.,it may be castered), can include a rotation counter that includes arotating permanent magnet. The magnetometer can be distanced from therotating permanent magnet by being located in a second wheel, such asany front wheel or a front wheel diagonally across from the rear wheelwith the rotating magnet, or on the handle of the cart. If themagnetometer is located in a second wheel, the second wheel can be freeof rotating magnets.

In addition to a rotating permanent magnet in a first wheel (e.g., arear wheel) that can indicate a speed and a distanced magnetometer thatcan indicate a directional heading, the navigation system can alsodetermine if the cart is moving forward or backward. There are differentways to do so. As one example, the magnet in the first wheel may passfirst and second sensors rigidly positioned with respect to theorientation of the cart, and the direction of rotation of the firstwheel can be determined based on whether the first or second sensor istriggered first. As another example, the angular position of therotating magnet is estimated using two magnetic field sensors atdifferent angular positions in a wheel PCBA. Given a known vectormagnetic moment of the rotating magnet, a possible angular position ofthe rotating magnet can be determined based on the magnetic fieldvectors at the two different magnetic field sensors. In someembodiments, the first wheel can be used to determine speed based on arotating magnet while forward/backward movement is determined by readinga magnetometer at a first location (e.g., on a handle) and amagnetometer at a second location (e.g., in a second wheel).

In some embodiments, the magnetic field produced by the rotating magnetat the magnetometer is estimated and subtracted from the total fieldmeasured by the magnetometer. An inexpensive way to do this is toextrapolate the angular motion of the rotating magnet (e.g., estimateangular velocity versus time from timestamps of rotation detection) andintegrate that function with respect to time from the most recentrotation detection to the present time. As described herein, motiondetection can be used to wake up the smart positioning system from alow-power (e.g., sleep) state. This can help preserve energy consumptionby the smart positioning system. In some embodiments, the second wheel(e.g., a front wheel) can also include a system for waking the processor(e.g., processor 370 of FIG. 3) that does not depend on rotationdetection. For example, a motion detection system could use anaccelerometer such as the LIS2DE from STMicrosystems NV (Geneva,Switzerland) to determine that the wheel has moved. Another examplesystem for waking the processor that does not depend on rotationdetection includes periodically waking the processor 370 FIG. via aninternal timer and activating the communication system of the secondwheel (e.g., the communication system 365 of FIG. 3) to listen for amessage from the other (e.g., rear) wheel (e.g., smart locking wheel 215of FIG. 3), indicating that the rear wheel has detected a rotation (atwhich point it is inferred that the entire cart is in motion).

c. Gyroscope in Wheel or Navigation Module

A cart can include a gyroscope to use in navigation and to enhance deadreckoning navigational accuracy, for example, as previously described inthe section entitled Gyroscope in Wheel or Navigation Mode. Gyroscopescan determine instantaneous motion and direction. An example gyroscopeis a MEMS gyroscope such as the LSM6DSL from STMicrosystems (Geneva,Switzerland). However, gyroscopes can use relatively large amounts ofpower, and constantly powering a gyroscope can be unsuitable for certainapplications that are highly sensitive to battery life, such as a smartlocking wheel.

Some systems can improve battery life by selectively operating thegyroscope for limited time periods instead of continuously operating thegyroscope. The gyroscope can be activated in response to determiningthat one or more of the other navigation systems are not functioningcorrectly. For example, a magnetometer guided navigation system (e.g.,as described for carts with front and rear castered wheels) may detect adistortion to the geomagnetic field. For example, magnets in acellphone, metals in passing cars or trucks, and other magnets or metalsmay be positioned close to a magnetometer in a cart and cause such adistortion. After hard and soft iron magnetometer compensation has beenperformed (e.g., as previous described with respect to blocks 1220 and1216 in FIG. 12A), distortions in the magnetometer reading can often bedetected after a navigation system produces a cart heading ingeomagnetic field coordinates.

One or more factors can indicate that a magnetometer is not functioningcorrectly or encountering a magnetic field distortion. One factorincludes determining if a vertical component of a magnetometer output ischanging significantly or changing beyond a threshold vertical amount(e.g., changes greater than 0.5%, 1%, 3%, 5%, 10%, 20%, or more).Another factor includes determining if a vector magnitude of themagnetometer output is changing significantly or changing beyond athreshold magnitude amount (e.g., changes greater than 0.5%, 1%, 3%, 5%,5%, 10%, 20%, or more). Another factor includes determining if themagnetometer output indicates a yaw rate that does not correspond to alow pass filtered y-axis acceleration (e.g., deviates by more than athreshold amount such as greater than 0.5%, 1%, 3%, 5%, 5%, 10%, 20%, ormore). Another factor includes detecting changes in the magnetometeroutput while the cart is at rest (e.g., deviates by more than athreshold amount from the measured or expected resting value, such as bygreater than 0.5%, 1%, 3%, 5%, 5%, 10%, 20%, or more). The numericalvalue of change that is appropriate may depend on the particular usagescenario. For example, when the cart is indoors, a greater level ofvariation is expected due to the proximity of ferromagnetic shelving andsimilar structures, but is on the order of a few percent.

As another example of a navigation system that may not always functioncorrectly, a photosensor in a light based navigation system (e.g., asfurther described with reference to FIGS. 19 and 20) may be covered up(e.g., a shopper places a paper shopping list over the photosensor). Asanother example, two or more navigation systems can indicate conflictinglocations.

In response to one or more navigation systems not operating properly orindicating conflicting locations or some other error, the gyroscope canbe powered on and used to improve the accuracy of the dead reckoningsystem or other navigational system. Otherwise, the gyroscope can bepowered off or put in a sleep mode, reducing power consumption.

When powered up, the gyroscope can provide an alternative and morereliable source of yaw rate. If the gyroscope is not mounted in theplane of motion of the cart, a three-axis gyroscope can be used to findthe cart's yaw rate, with the three individual gyroscope axes beingcombined according to the standard coordinate rotation (such asdescribed with respect to block 1208 of FIG. 12A). If the gyroscope ismounted in the plane of motion, a single axis gyroscope can be used tofind the cart's yaw rate.

The gyroscope can be left powered up until a sufficient period of timehas elapsed during which none of the indications of the magnetometerreading is being influenced by something other than the geomagneticfield have been seen.

d. Determining Cart Weight from Vibration Signatures

It can be advantageous to determine an estimate for the weight of acart, for example, to determine whether a shopping basket of a cart isloaded or unloaded. Cart theft prevention logic (see, e.g., the exampleexit detection flowchart 600 described with reference to FIG. 6) candepend, at least partly, on the estimated cart weight (or the estimatedweight above an unloaded cart weight), which can serve as a proxy forwhether a user is attempting to leave a retail store with a cart loadedwith unpurchased merchandise (a potential theft situation) or whether auser is leaving the store to return an unloaded cart to a cart corral (anon-theft situation). In a potential theft situation, a wheel may belocked (see, e.g., block 652 of the flowchart 600), whereas in anon-theft situation, the wheel may not be instructed to lock. As anotherexample, in a potential theft situation, since the cart load may be acustomer's child (who may be sitting in the cart) rather thanunpurchased merchandise, instead of locking the wheel, the logic atblock 652 may actuate an external security surveillance system (e.g.,surveillance system 1445 shown in FIG. 14) to take a picture or video ofthe customer leaving the store. As yet another example, at a boundary toa tracking area 114 (e.g., a boundary of a parking lot), it may bedesirable to prevent theft of the cart whether loaded or not.Accordingly, the exit detection logic may lock the cart wheel(s) at atracking area boundary regardless of the determination of whether thecart is loaded (or the cart loading determination may be omitted in suchregions).

The weight of the cart can affect other features. For example, aspreviously described, a shopping cart may lock its wheels whendetermining that a shopping cart is exiting a store without passing orstopping by the checkout lanes. However, the cart may be allowed to exita store without locking its wheels if the cart's weight indicates thatthe cart is empty. As another example, the speed or force at whichbrakes engage to stop a cart may depend on the weight of the cart.Heavily weighted carts may have brakes applied with greater speed orforce to slow down the momentum of a loaded cart. Unloaded carts mayhave brakes applied more slowly or with lower force so that the cartdoes not change momentum too suddenly.

A weight of a cart can be determined based on a vibration response ofthe cart. For example, a loaded cart vibrates with a different vibrationsignature after it crosses over a discontinuity (e.g., a tile joint,exit bump, etc.) than a lighter cart (e.g., an unloaded cart). Bymeasuring the vibration signature induced by a discontinuity, the smartpositioning system can estimate the mass of the cart or the load of thecart or simply determine whether or not the cart is loaded (orunloaded). Because the mass of the unloaded cart is known, the mass ofthe load in the cart can be estimated in some embodiments. In someembodiments, the system determines from the vibration response whetherthe cart is loaded or unloaded but does not make an estimate of theamount of the load (or the weight of the cart), because the anti-theftor navigation logic described herein may only need information onwhether or not the cart is loaded (and not the amount of the load).

The presence or absence of a significant load (e.g., larger than 2 kg,larger than 5 kg, larger than 10 kg, larger than 15 kg, larger than 20kg, larger than 25 kg, larger than 30 kg, larger than 50 kg, etc.) in acart 205 can often be determined based at least in part on thevibrational signature of the shopping cart in response to shockimpulses, in particular impulses along the Z-axis of the coordinatesystem 230 shown in FIG. 2.

A load in the basket that is on the same order of mass or greater thanthe mass of the empty cart will behave similar to a cantilevered mass,again particularly in the Z-axis. The energy of the ringing oscillatorcomprising the load mass and the (semi)-rigid arm created by the cartbasket is mostly concentrated in the Z-axis. However, the highestamplitude of acceleration/vibration/ringing is in the X-axis, mostlybecause there is much more compliance for the cart to move with respectto the ground in the X-axis. For example, the entire frame of the cartwobbles by a small amount on the wheel axles. Accordingly, thesurprising and unexpected result of the experiments described withreference to FIGS. 21A and 21B is that the vibration signature manifestsitself most strongly in the X-axis vibration data, rather than theZ-axis vibration (the direction in which the impulsive shock initiallyoccurs).

Thus, a vibration signature should show ringing after an impulse in thepositive Z direction. The vibration signature can be measured, forexample, by a smart positioning system 210 shown in FIG. 2 at the handleof the cart 205. Accordingly, a weight of a cart can be determined basedon the vibration responses of the cart. After passing over adiscontinuity (e.g., a tile joint), a loaded cart vibrates with adifferent vibration signature than an unloaded cart.

The hardware shown in FIG. 4, including the a three axis accelerometer410, other vibration sensor(s) 415, and processor 425, that are used toprocess vibrations for inferring wheel rotation can be used to measureimpulses along the Z axis and ringing (post-impulse) along Z, X, orY-axes. As will be described, the X-axis vibration data can provide auseful signature to assist in determining whether the cart is loaded ornot.

FIG. 21A shows an example of a time domain three axis acceleration of anunloaded steel framed 53 pound shopping cart (Model M90Z from UnarcoIndustries (Wagoner, Okla.)) going over a tile joint at a speed of about1.0 meters/sec. The data was measured using the same experimental setupas for the data in FIG. 11B. After an initial impulse, the cartexperiences significant ringing along the X-axis and fast ringing alongthe Z-axis (at substantially the same time).

FIG. 21B shows an example of the time domain three axis acceleration ofthe same cart as in FIG. 21A, but with a 5 kg load in the front of thebasket going over the same tile joint at the same speed. After aninitial impulse, the cart experiences minor ringing along the X-axis andslow ringing along the Z-axis.

In comparing the vibration signatures shown in FIG. 21A and FIG. 21B,significant ringing in the X-axis acceleration occurs in the unloadedcart shortly after (e.g., about 1 to 3 ms) the Z-axis impulse from thewheel dropping into a joint, compared with the much lower degree ofX-axis ringing in the loaded cart. For example, the amplitude of theX-axis ringing in the unloaded cart is about 2-3 g's initially (e.g.,decaying over several milliseconds), and the ringing occurs with aperiod of a fraction of a millisecond (frequency of 1-2 kHz). Incontrast, the loaded cart has minor ringing in the X-axis with aninitial amplitude of less than about 0.5 g (e.g., 4 to 6 times loweramplitude than unloaded cart). Thus, some embodiments, analyze vibrationsensor data to find a vibration signature in the X-axis data anddetermine whether the cart is loaded or unloaded from the X-axisvibration signature. For example, the vibration signature of an unloadedcart may comprise an X-axis vibration having a frequency greater thanabout 1 kHz (up to about 5 kHz) and an amplitude greater than about 1 g(or greater than 2 g or greater than 3 g). The vibration signature of aloaded cart may comprise an X-axis vibration having a frequency greaterthan about 1 kHz (up to about 5 kHz) and an amplitude less than about0.5 g (or less than about 0.2 g). The X-axis vibration signature of aloaded or unloaded cart may occur a time period of about 1 ms to about 5ms (or 1 ms to 10 ms) after a Z-axis impulse (in a range from about 0.5g to about 3 g that lasts for a period of less than about 10 ms) ismeasured. Thus, in some embodiments, the magnitude of the X-axisacceleration of an unloaded cart is above a vibration threshold (e.g.,about 1 g) and the magnitude of the X-axis acceleration of a loaded cartis below the vibration threshold.

Given the large variation in shopping cart mechanical designs, otherspecific vibration signatures may characterize loaded and unloadedcarts, and variations can occur in the signatures. However, the datashown in FIGS. 21A and 21B suggests that for common cart designs, theringing signature between a loaded and unloaded cart is easilydetectable from the vibration sensor data. For example, carts withplastic (e.g., ABS or ABS-polycarbonate blends) baskets (and a metalframe) are expected to ring less than a cart with a metal basket (and ametal frame), because the coupling of the initial impulse from the tilejoint into the frame leads to a coupling (e.g., metal to plastic) whichis diffuse (e.g., multiple mechanical points of contact with randomlydistributed phase) and somewhat absorptive. Two level basket carts areexpected to have two natural ringing frequencies, one for each basket.

Accordingly, analysis of the vibration sensor data can determine whetherthe cart is loaded (or not), where a load can be a few kg or greater.Other cart signatures can be used (additionally or alternatively) todetermine whether a cart is loaded or unloaded. For example, thevelocity signature of a cart can depend on cart load. A shopper pushingan unloaded cart can get the cart up to a typical speed more easily thana loaded cart (with increased mass that needs to be accelerated by theshopper). By examining shopper usage statistics, typicalacceleration/deceleration times, speeds, human-propelled forces oncarts, distances for loaded versus unloaded carts can be determined andcompared to the corresponding measured value (in a particular situation)to determine whether or not the cart is loaded or unloaded. As anexample, shopper usage statistics can be used to establish that atypical human shopper can apply a certain amount of force to propel acart to reach a typical terminal cart speed (e.g., similar to walkingspeed). Assuming the human force, F, and the terminal cart speed, v, areapproximately the same whether the cart is loaded and unloaded, anestimate for cart mass M is M=(F/v) t, where t is the measured time toreach the terminal speed (from rest). With the ratio (F/v) being roughlyindependent of whether the cart is unloaded or loaded, measurements ofthe time t can be used to infer an approximate mass M of the cart or atleast whether the cart is likely to be loaded or unloaded.

Additionally or alternatively, a characteristic initial acceleration a₀of an unloaded cart associated with a specific shopper may be determinedas follows. From an initial state where the cart is inferred to beprobably empty, e.g., from entering the store from outside, or from thecart having been at rest for a specific time, e.g. one hour, or in alocation known to typically contain only empty carts such as a cartcorral, an initial unloaded acceleration a₀ may be measured from thefirst forward motion of the cart from, preferably from an indoor stop.

The acceleration a₀ can be measured from rest to a specific cartvelocity v₀ which is less than a typical terminal cart velocity, e.g.0.5 m/sec. The acceleration can be determined as a₀=v₀/t, where t is thetime from rest to the terminal velocity. From observations of shoppersstarting up loaded carts, it has been observed that the acceleration ofa loaded cart is typically much less (e.g., less than 75%, 50%, 25%,etc.) than the acceleration of an unloaded cart towards the beginning ofthe acceleration process. In some cases, the shopper may “lean into” aloaded cart to get it to move faster, which may increase theacceleration. Accordingly, measurement of a₀ (particularly early in theacceleration process) can provide a clear signature of whether the cartis loaded or unloaded.

In some implementations, at each start from an indoor stop, the averageacceleration a can be compared to a specific a₀ associated with thecart/shopper combination, and if a is substantially less than a₀, e.g.less than 75%, or 50%, or 25%, of a₀, then the cart is provisionallyinferred to be loaded. The initial accelerations of unloaded carts maybe different in the forward and backward direction. Also, decelerationsmay be different for loaded and unloaded carts, in particular, anaverage deceleration d from v₀ to rest can be much greater in magnitude(e.g., greater than 125%, 150%, 175%, etc.) with loaded carts than withunloaded carts, because a shopper may instinctively rotate backwardtoward the cart as it slows.

As described above, in response to determining whether or not the cartis loaded, the cart exit detection logic (e.g., beginning at block 604of FIG. 6) may modify the lock sequence (e.g., block 652), for example,by locking the wheel for loaded carts but not for unloaded carts,actuating a surveillance imaging system (in addition to or as analternative to locking a cart wheel), etc.

e. Multi-Level Navigation (3-D Navigation)

It can be advantageous to determine and use the present altitude of acart. For example, the cart may operate in a multi-floor structure,where different floors have different shopping cart containmentboundaries (e.g., boundary 118 of FIG. 1), payment points (e.g.,checkout lanes previously described in paragraph [0287] or as describedin U.S. Pat. No. 8,463,540), floor maps, aisles, magnetic fieldconfigurations, access permissions (e.g., shoppers may be permitted totake carts to parking levels but not to residential or office levels ofthe structure), etc. Accordingly, different cart containment logic canbe used for different levels of a structure. For example, aconfiguration file of the containment system can include a multi-levelmap of the structure (similar to the ground-plan 1400 described withreference to FIG. 14).

The multi-level maps can be include information on a plurality ofsurfaces, e.g. floors of a building and can include with ramps,escalators, elevators, or other vertical transportation paths betweenthe different floors. Ground plans such as ground plan 1400 of FIG. 14can be provided for multiple floors in the multi-level structure andaccess permissions can depend on, e.g., the floor, the transportationpath (e.g., a cart may be permitted in an elevator but not on anescalator), etc.

A variety of vertical position detectors can be used to determine thevertical position of the cart. The vertical position detector can bepart of the smart positioning system 210 as shown in FIG. 3. Examples ofvertical position detectors include barometric pressure sensors,altimeters, accelerometers, beacons, etc. In some embodiments, a cartcan include a vertical position detector 337 (shown in FIG. 3) such as abarometric pressure sensor (e.g., an MPL3115A2 from NXP (Eindhoven, theNetherlands)), which can be used to determine altitude (or change inaltitude) of the cart. Pressure sensors can have a differential accuracyon the order of 10 cm. One or more barometric pressure sensors at fixedreference points (e.g., at the front door of the first floor, anelevator door of other floors, top and/or bottom of an escalator, etc.)can provided a temperature-compensated reference pressure. The referencepressure can be communicated to a processor in the cart, which cancompare a barometric reading from a barometric pressure sensor on thecart to the reference pressure to determine the altitude of the cartrelative to the altitude of the reference pressure.

In some embodiments, a cart can include an accelerometer (e.g., theaccelerometer 410 of FIG. 4). A vertical acceleration indicated by theaccelerometer can be used to determine vertical travel in a variety ofcases. For example, in a first case, when a cart is moving bothvertically and horizontally such as on an inclined ramp between floors,the vertical component of the cart's acceleration can be integrated(twice, from acceleration, to speed, to displacement) to yield avertical displacement. In a second case, a cart's travel in an elevatorcan be inferred from the combination of significant, relatively smoothvertical acceleration (with a magnitude of typically a few hundredths toa few tenths of a g) for a few seconds followed by a smooth deceleration(having an opposite sign as compared to the vertical acceleration and acomparable magnitude), with little or no detection of rotation orlateral movement (in directions perpendicular to the verticaldirection). A vertical acceleration time series can be integrated toyield nominal vertical travel that can be matched to the closest flooraltitude. By assuming that the elevator stops on a defined floor, anyintegration error can usually be ignored and the barometer can berecalibrated to the known altitude of the floor.

In some embodiments, markers can be used to determine the verticalposition of a cart. Some buildings have a shopping cart conveyor systemsuch as the Cartveyor™ from Pflow Industries (Milwaukee, Wis.) to movecarts between floors. Such conveyors are also known as travelators. Suchconveyors usually inhibit the cart wheels from rolling or rotating whilethe cart is in the conveyor. These conveyors have an entrance and anexit. These entrances and exits can be included in the installation map(see, e.g., the ground plan 1400, which can be adapted to represent oneor more floors other than a ground level in a structure). The smartpositioning system can determine that the cart is in such a conveyor bythe combination of a dead reckoned position close to one of theentrances to the conveyor followed by both vibration (from the conveyor)and substantial absence of wheel rotation. In some embodiments, specificlocation beacons (e.g., the RF beacon 395 in FIG. 3) and/or entry/exitmarkers (e.g., as the fixed feature 385 in FIG. 3) can be used to signalin the configuration file (e.g., such as Table 1) indicating which floorthose beacons and/or markers are located on.

f. Multi-Level Magnetic Measurements

A multi-level magnetic field map can be used to determine the locationof a cart. The magnetic field map can be generated, for example, byusing a magnetometer to record the magnetic signatures of an area suchas inside retail store 110 of FIG. 1 or in a parking lot. This caninclude, for example, down the various aisles of a retail store. Asdescribed with reference to paragraphs [0291]-[0292], some embodimentsof the navigation system can use correction vectors to compensate fordistortions in the geomagnetic field caused by metal or magneticstructures inside a building. The correction vectors can compensate atleast partially for horizontally or vertically stratified magneticanomalies in the store.

In some embodiments, carts can use multiple magnetometers (e.g., 2, 3,4, 6, or more) to improve magnetic navigation accuracy. Magnetometerscan be used to detect a magnetic field that matches with a magneticfield for a particular location on a magnetic field map. Magnetometerscan also be used to determine the directional heading of a cart, whichcan be used for dead reckoning. Since the magnetometers are typicallyfixed to a frame of a cart at a particular height above the ground or ata fixed (or rotating) position inside a wheel of the cart, themagnetometers can provide information about the magnetic field at thecorresponding heights inside the structure. Thus, the multiplemagnetometers provide information on vertical stratification of themagnetic field at different heights above the floor level, and as thecart is moved horizontally around the structure, the magnetometersdetect the horizontal stratification of the magnetic field. Thenavigation system can store information on the magnetic signature of thestructure (e.g., locally in the smart positioning system or in a memoryin a remote computing, base station).

In some embodiments, the cart includes two (or more) smart positioningsystems 210 that communicate with each other (via wired or wirelesstechniques), and each contains a magnetometer coupled rigidly to thecart frame. For example, one magnetometer can be mounted to a carthandle (e.g., handle 1610 of FIG. 16) and a second magnetometer can bemounted to the front rail of the basket of the cart.

In some embodiments, a single smart positioning system 210 is mounted tothe cart, such as on the handle, basket, etc. In addition, one or moremagnetometers can be included in one or more of the wheels or casters.The wheel-mounted magnetometers could be part of a smart locking wheelsuch as smart locking wheel 215 of FIG. 2, or part of a standalonemagnetometer component containing at least a magnetometer associatedwith a processor, communication link, and power source (but without thelocking mechanism).

An implementation of such a wheel could include a KMX62 6-axismagnetometer/accelerometer from Rohm Kionix (Kyoto, Japan), a MKW31Z MCUwith 2.4 GHz transceiver from NXP (Eindhoven, the Netherlands), and abattery, molded inside a wheel and configured to rotate with the wheel.The accelerometer function of the KMX62 can be used to infer the presentangular position of the magnetometer, so that the magnetometer outputcan be transformed to the local horizontal reference frame. Such arotating magnetometer samples the local magnetic field over a range ofheights corresponding to the diameter of its circular path.

For extra accuracy, a cart can (optionally) have multiple magnetometersat different locations in the cart body and magnetometers in one or morewheels or casters. The one or more wheels or casters can include acommunication system to communicate magnetometer measurements to thesmart positioning system such as smart positioning system 210 of FIG. 3.

Magnetometer navigation can be used with dead reckoning navigation (orother navigation systems (e.g., with lighting signatures)) both indoorsor outdoors. For example, dead reckoning systems may be primarily reliedupon when the geomagnetic field is significantly distorted. Thegeomagnetic field can be significantly distorted, for example, atoutdoor positions near a building. Medium sized buildings can have adistorted geomagnetic field within about 3 meters outside of thebuilding, and larger buildings made with more metal can distort thegeomagnetic field for up to 10 meters or farther. However, withoutsignificant geomagnetic distortions, a magnetometer can be calibratedwithin about 0.3 degrees or less than 1 degree, and magnetometernavigation can be accurate within about 1 or 2 degrees of heading error.In other cases without significant geomagnetic distortions, magnetometercalibration and magnetometer navigation can achieve varying levels ofaccuracy based on other factors such as component design, temperature,etc.

The magnetic field map can be a multi-layer map. The different layerscan be recorded at the different levels at which magnetometer on anavigating cart might be positioned. For example, a first magnetic fieldmap level may include a magnetic signatures at 2-3 inches off the groundof a first floor if magnetometers are located a 2-3 inches off theground in a wheel of a cart. As another example, a second magnetic fieldmap level may include magnetic signatures at 3 or 4 feet off the groundof a first floor at the height of a magnetometer located on the handlesof a cart. Additional magnetic field map level may be made for thebasement, second, third, and additional levels of a building. Anadditional magnetic field map can be recorded for transitional areasbetween levels, such as along cart escalators or inside of elevators.The magnetic field map can be included in a floor plan 1400 or siteconfiguration file.

As described herein, the multi-level magnetic field map can includemagnetic signatures at various heights for different locations, and thedead reckoning system can be configured to set its position to alocation in the magnetic field map upon detecting a magnetic signaturecorresponding to the location.

A location determined based on a mapped magnetic signature can be usedin conjunction with one or more other navigation systems. For example, adead reckoning system can be used to determine that a cart is at a firstlocation, and a second location based a mapped magnetic signature can beused to confirm the accuracy of the first location.

In some embodiments, each navigation system determines a location and aconfidence level that the cart is at the location. For example, a deadreckoning system can be used to determine that a cart is at a firstlocation with 90% confidence, and a second location is determined with90% confidence based a mapped magnetic signature. If the first andsecond locations match, the confidence level can increase to a numbergreater than 90% (e.g., 95% or 100%). Thus, the location of the cart canbe determined as a combination of the first location and the secondlocation, optionally weighted by the confidences. If the first andsecond locations do not match, then in some embodiments, a thirdlocation between the first and second locations (e.g., a (weighted)average of the first and second locations) can be determined with alower confidence. If the first and second locations do not match, thenin some embodiments, a first navigation system can backtrack andrecalculate a result using data from the second navigation system. Insome embodiments, if the confidence of a position falls below athreshold value, then additional navigational systems can be used toincrease the confidence level, such as by expending additional power toturn on and use a gyroscope. Examples of backtracking are described withreference to FIG. 22.

The magnetic fingerprint of an area can change. For example, metalshelving can be rearranged in a store, which can affect the magneticfingerprint detected by a magnetometer. The magnetic fingerprint andnavigation history data can be transmitted to a computer that cananalyze the magnetic fingerprints collected along a cart path and detectchanges in the fingerprint. New magnetic field maps can be generated,communicated to the carts (e.g., from a remote base station), and storedin the memory of a cart. The magnetic field map data over time (magnetichistory) can be analyzed to learn magnetic signatures in the structureusing various machine learning, artificial intelligence, or neuralnetworks.

g. Navigation Using Lighting Signatures

In addition or as an alternative to the magnetic and RF signaturesdescribed elsewhere, signatures of light sources in known locations canbe used to assist in determining the location or directional heading ofa cart. Measurement of light signatures can be used as to supplementdead reckoning location information. One example of fixed light sourcesin known locations includes lights located inside of a building (e.g.,overhead fluorescent lights in a store). Another example includes lightsin a parking lot, which may be turned on at night. Data including a mapor locations of light sources and the characteristics of the lightsources can be provided to a smart positioning system such as smartpositioning system 210 of FIG. 3. The map or locations of light sources(and optionally their properties such as heights above the plane of thelight detector, optical power, or angular dependence of optical power)may be part of a floor plan 1400 or included in a site configurationfile (see, e.g., Table 1) for the environment in which the cart islocated. The floor plan 1400 or the site configuration file can bestored in non-transitory memory in the smart positioning system.

FIG. 19 shows an example system 1900 of a cart navigating outdoors usinglighting signatures. In FIG. 19, light emitted from a point light source1910 such as a parking lot light reaches a cart 1905. The cart 1905 isseparated from the point light source by radial distance r, includingcomponents of horizontal distance d and vertical distance h. A polarangle θ is also shown in FIG. 19 (measured from the upward, verticaldirection).

The cart 1905 can include an opaque housing around a photosensor and alight pipe positioned as an aperture through the opaque covering suchthat the photosensor is configured to detect ambient light passingthrough the light pipe. The housing, photosensor, and light pipe can beused as a light detector 333 in the smart positioning system 210 shownin FIG. 3. For example, the light pipe (e.g., a light transmissivematerial such as polycarbonate) can be formed in a surface of the smartpositioning system 1605 shown in FIG. 16 and direct light to aphotosensor included on a PCBA 1705 inside the system.

An example light source 1910 is mounted at a height h above the plane ofthe horizontal light pipe aperture at a horizontal distance of d andtherefore radial distance r=√{square root over (h²+d²)}. The examplelight source uniformly emits light in a downward hemisphere such thatthe irradiance E_(e) associated with the light source is independent ofpolar angle θ and azimuth φ (e.g., coming out of the page in FIG. 19)for angles of interest. To better aid an understanding of the concepts,the example in FIG. 19 shows no other light sources contributesignificantly to the optical flux through the light pipe aperture, andall other sources combined contribute less than a few percent points(e.g., 1%, 3%, 5%) of the flux through the light pipe aperture. Theoptical power P received through aperture A is

$\begin{matrix}{P = {P_{0}\frac{A}{2\pi\; r^{2}}\cos\;\theta}} & (2)\end{matrix}$where P₀ is the total optical power of the source. The optical power Preceived at the light pipe aperture can be measured with a photosensorsuch as the APDS-9008 from Broadcom, Limited (San Jose, Calif.).

In the following example, the coordinates of the cart are measured in anX_(L), Y_(L) Cartesian coordinate system, which is fixed in the store(see FIG. 20, with Y_(L) parallel to the aisle and X_(L) perpendicularto the aisle). These coordinates are different from the cart-centeredCartesian coordinates described herein that may be used by the smartpositioning system to perform dead reckoning position estimates.

An example cart 1915 starts from a position x₁,y₁ (in the store-centeredcoordinate system) where the received optical power is P₁, and a deadreckoning system estimated position of the cart 1915 at

. As the cart 1915 travels to a second position x₂,y₂, the deadreckoning system determines that the cart 1915 travels in an estimateddirection ρ for distance d, to a point

. At the second position x₂,y₂, the received optical power is P₂.

In some cases, the errors in ρ and d can be small relative to theaccumulated dead reckoning error included in

, and navigation using lighting signatures can be more accurate thandead reckoning without lighting signatures. The most probable truestarting location can be determined by reducing or minimizing the errorterm by finding ∈_(x) and ∈_(y) in equation 3 that reduces or minimizesthe error term in equation 4, subject to the constraint in equation 5.∈_(x) =x ₁−

and ∈_(y) =y ₁−

  (3)P ₁(x ₁ ² +y ₁ ²)^(3/2) −P ₂(x ₂ ² +y ₂ ²)^(3/2)  (4)x ₂ =x ₁ +d cos ρ and y ₂ =y ₁ +d sin ρ  (5)

The error term can be reduced or minimized by solving equations 3-5analytically or using numerical optimization methods (e.g., linear ornonlinear programming, least squares, Newton's method, gradient descent,etc.).

As discussed, some embodiments can use numerical minimization methods inaddition to or instead of analytical methods. In some cases, numericalminimization methods such as gradient descent can be more resilientagainst errors in measurements. The gradient descent method can be usedwhen the light source output is not independent of polar angle θ andazimuth φ, as long as the functions ƒ1(θ) and ƒ2(φ) which give theangular dependence according to equation 4 are known numerically and aresingle peaked over the range of angles of interest, where the receivedoptical power is:

$\begin{matrix}{P = {P_{0}\frac{A}{2\pi\; r^{2}}\cos\;\theta\; f\; 1(\theta)f\; 2{(\varphi).}}} & (6)\end{matrix}$

Given a set of point light sources at known x-y locations, heights ofthe light sources (e.g., above the plane of the light detector or abovethe floor), optical power, or angular dependence of optical power, astarting point and optical power measured at various points along a pathtraveled by a cart can be used to find the absolute location of the cartat a point in that path by reducing or minimizing a total errorfunction, again by means of an optimization algorithm such as gradientdescent. The weights of individual terms in the error function to bereduced or minimized can depend on the accuracy of the individual lightsources locations, optical power, and angular dependencies of opticalpower.

Additional checking of the time history of the photosensor output may bevaluable to confirm that the path from the light source to the lightpipe aperture was not blocked, e.g., the time rate of change of thephotosensor output should be consistent with the known velocity ordirection of motion of the cart. Deviations from such consistency can bedetermined and data acquired during the inconsistency can be omitted orweighted less heavily in the optimization calculations.

These types of calculations can be performed by the processor and memory325 in FIG. 3. However, processing these types of calculations can use alarge amount of energy. It may be desirable to perform the computationat an offboard computing system (e.g., a base station), with the smartposition system communicating raw or preprocessed measurements via thecommunication system 330 of FIG. 3 and then receiving an updatedposition estimate. These types of calculations can also be performedwhen the rotation of one or more wheels indicates motion, and theprocessor can stop performing such calculations when rotation of wheelsindicates that the cart is at rest.

FIG. 20 shows an example system 2000 of a shopping cart 2005 navigatingindoors using lighting signatures. The shopping cart 2005 includes asmart positioning system 210 (e.g., as described with respect to FIG. 2and FIG. 3). The smart positioning system 210 includes a light detector333 comprising a light pipe aperture and a photosensor. The cart movesinside an example grocery store that includes light fixtures 2015A,2015B, 2015C, such as fluorescent or LED light tubes. The example lightfixtures in this example include two tubes in parallel with a smallseparation (e.g., less than 10 cm), mounted above and parallel to theaxis of each aisle. Merchandise shelves line the sides of the aisle. Insome embodiments, the light pipe aperture may be in a range from about 1mm² to 100 mm² to acquire light for a sufficient photosensor signal.FIG. 20 illustrates three lighting fixtures, such as model P7137-30STRfrom Progress Commercial Lighting (Greenville, S.C.) each containing two17 W T8 fluorescent tubes, with centers spaced 122 cm (48 inches) apartlocated at a height 2 meters above the light pipe aperture.

A shopping cart's motion passing under one of these fixtures can producea peak in the photosensor output as the photosensor of the cart passesunder the centerline of the fixture, independent of the crossing angle.The peak may be relatively sharp. It is expected that the peak sharpnessas function of the aperture X_(L) coordinate will be independent of thecrossing angle, although the sharpness of the peak may generallydecrease somewhat as a function of increasing distance of the centerlinecrossing in the Y_(L) coordinate (e.g., the farther away the aperture isfrom the center of the lighting fixture at the time the aperture crossesthe centerline that runs down the middle of the string of threefixtures). The degree of “blurring” of the peak may depend on thespecific characteristics of the lighting fixtures (for example,fluorescent tubes versus LED tubes of equal nominal luminosity), andindeed in some cases there may be no detectable broadening of the peakwith significant off-center crossings. The reliable feature of thelighting signature is the presence of the peak.

Note that if the photosensor is sampled a rate that is high relative tothe horizontal crossing speed, for example greater than about 100samples per second with a crossing speed of one meter/second, it issometime possible for two separate peaks to be resolved, the first peakas the aperture passes directly under the first tube of the dual tubefixture, and the second peak as the aperture passes directly under thesecond tube of the dual tube fixture. Since the tube centers aretypically much less than ten centimeters apart, only a very highsampling rate will resolve the double peak.

h. Multi-Navigation System Synergy

The combined use of multiple navigation systems can yield synergiesbeyond the sum of the individual parts. As one example of synergy, onenavigation system can be used to determine if another navigation systemis not functioning correctly, and the functional navigation system canbe used. For instance, a dead reckoning system can be used inconjunction with a navigation using lighting signatures to determine ifthe photosensor is blocked. If the dead reckoning system determinesmovement while no lighting changes are detected by the photosensor, thiscan indicate that the photosensor and/or the light pipe is covered,turned off, or malfunctioning. The time rate of change of thephotosensor output should be consistent with the known velocity anddirection of motion of the cart. Different navigation systems candetermine location, heading, and speed, and minor discrepancies betweendifferent systems can be weight averaged based on known error rates todetermine an average estimated location, heading and speed. Largerdiscrepancies can indicate that a navigation system is not workingproperly, such as if the light pipe was covered for a period of time,and when discrepant navigation system resumes working, it can use thelatest position, speed, and directional information from a differentnavigation system to begin navigating again.

FIG. 23 shows another example of synergy where multiple navigationsystems can be used to determine a more accurate location of a cart withan improved confidence. A cart 2305 can use both a dead reckoningnavigation system and RSSI as discussed in the section entitledRSSI-Aided Dead Reckoning.

A cart 2305 starts a first location 2310. The dead reckoning systemestimates that the cart moves to a second location 2315. However, thedead reckoning system may accumulate errors at a known rate such that afirst confidence level in the second location can be relatively low (50%confidence, confident within 4 meters, etc.). Different embodiments mayuse different confidence systems.

An access point 136, such as previously described with respect to FIG.13, may broadcast a signal to the cart 2305. Based on RSSI calculations,the cart can determine that it is located on an arc at a fixed radialdistance 2320 away from the access point 136 with a second level ofconfidence.

Based on the combined information from the dead reckoning system, it canbe determined that the cart is somewhere on or between the estimatedlocation 2315 and the arc 2320. For example, the data can be combined todetermine that the cart 2305 is at location 2325. Furthermore, theconfidence level that the cart is at location 2325 can be higher thanthe first confidence level and/or higher than the second confidencelevel. For example, the navigation system can determine that the cart2305 is at location 2325 with a 90% confidence level or within +/−1meter.

Some functionality, such as activating the brakes on a shopping cartwhen shoplifting is suspected, can be performed when a minimumconfidence threshold of positions is determined.

Although FIG. 23 is described with respect to dead reckoning and RSSI,it will be understood that the concepts can be applied to othercombinations of navigation systems.

Additional Aspects

Any of the navigation system functionalities can be used with any of theother functionalities described herein. For example, any of thetechniques for using navigation history and backtracking, dual swivelcastors, gyroscopes, determining cart weight or whether the cart isloaded or unloaded, multi-level (3D) navigation, multi-level magneticsensors, navigation with lighting signatures, RF data (e.g., RSSI),magnetometer data, or vibration data can be used alone or in anycombination with each other or with other navigation (e.g., magneticdead reckoning) or anti-theft techniques. For example, any of theelements of any of the following aspects can be combined with any of theother aspects. All possible combinations and subcombinations of aspects1-108 are contemplated herein.

In a 1st aspect, a navigation system for a wheeled object, thenavigation system comprising: a vibration sensor; and a hardwareprocessor programmed with executable instructions to analyze vibrationdata from the vibration sensor to determine a rotation rate of a wheelof the wheeled object.

In a 2nd aspect, the navigation system of aspect 1, wherein the hardwareprocessor is programmed to analyze a spectrum of the vibration data.

In a 3rd aspect, the navigation system of aspect 2, wherein the hardwareprocessor is programmed to identify a first peak in the spectrum, thepeak associated with vibration data for vibrations in a forward orrearward direction of the wheeled object.

In a 4th aspect, the navigation system of aspect 3, wherein the hardwareprocessor is programmed to determine the rotation rate of the wheel tobe a harmonic frequency of the frequency of the first peak.

In a 5th aspect, the navigation system of aspect 4, wherein the hardwareprocessor is programmed to validate the determined rotation rate byanalyzing the spectrum for presence of a second peak at a harmonicfrequency of the first peak.

In a 6th aspect, the navigation system of aspect 5, wherein the hardwareprocessor is programmed to analyze the spectrum for presence of thesecond peak at a first odd harmonic frequency of the first peak.

In a 7th aspect, the navigation system of any of aspects 1 to 6, whereinthe hardware processor is programmed to estimate a forward or rearwardspeed of the wheeled object based on the determined wheel rotation rateand a circumference of the wheel.

In an 8th aspect, the navigation system of any one of aspects 1 to 7,wherein the navigation system is configured to receive informationrelating to a reference position and the hardware processor isprogrammed to reset the position of the wheeled object based at least inpart on the reference position.

In a 9th aspect, the navigation system of any one of aspects 1 to 8,wherein the hardware processor is further programmed to count regularboundaries on a surface over which the wheeled object travels.

In a 10th aspect, the navigation system of aspect 9, wherein thehardware processor is programmed to analyze a time-domain series of thevibration data in a vertical axis.

In an 11th aspect, the navigation system of any one of aspects 1 to 10,wherein the hardware processor is programmed to apply a correctivemapping to the geomagnetic field to compensate for perturbations to thegeomagnetic field due to presence of magnetic elements.

In a 12th aspect, the navigation system of any one of aspect 1 to 11,wherein the hardware processor is further programmed to dynamicallychange modes of the DR position estimation method based at least in parton the vibration data.

In a 13th aspect, the navigation system of any of aspects 1 to 12,wherein the wheeled object comprises a human-propelled cart.

In a 14th aspect, the navigation system of aspect 13, wherein the DRsystem is mounted to a handle of the cart.

In a 15th aspect, a navigation system for a human-propelled cart, thenavigation system comprising: a magnetometer; an accelerometer; avibration sensor; a communication system configured to communicate witha wheel of a human-propelled cart, the wheel comprising a brakeconfigured to inhibit rotation of the wheel in response to receipt of alocking signal; and a hardware processor programmed to: estimate a speedof the human-propelled cart based at least in part on vibration datafrom the vibration sensor; and estimate a position of thehuman-propelled cart based at least in part on the estimated speed ofthe cart.

In a 16th aspect, the navigation system of aspect 15, wherein thehardware processor is programmed to determine, based at least in part onthe estimated position, whether the cart has crossed a containmentboundary, and in response to the determination, to communicate thelocking signal to the wheel.

In a 17th aspect, the navigation system of aspect 15 or aspect 16,further comprising a detector configured to detect an entrance signal oran exit signal indicative of whether the cart is entering or exiting astore, respectively.

In an 18th aspect, the navigation system of aspect 17, wherein thedetector determines whether the cart is entering or exiting a storethrough searching for a peak in a received signal strength indicator(RSSI) of the entrance signal or the exit signal.

In a 19th aspect, the navigation system of any one of aspects 15 to 18,further comprising an audible or visual indicator configured to providea notification to a user of the cart.

In a 20th aspect, the navigation system of any one of aspects 15 to 19,wherein the cart comprises a handle and the navigation system is mountedto the handle.

In a 21st aspect, the navigation system of any one of aspects 15 to 20,wherein the accelerometer is the vibration sensor.

In a 22nd aspect, the navigation system of any one of the aspects 15 to21, further comprising a temperature sensor.

In a 23rd aspect, the navigation system of aspect 22, wherein thetemperature sensor is physically close to the magnetometer.

In a 24th aspect, the navigation system of any one of aspects 1 to 23,wherein the hardware processor is further programmed to receive siteconfiguration data comprising information associated with one or moreof: (1) a containment boundary, (2) an entrance or an exit, (3) anindoor area of the site, (4) an outdoor area of the site, (5) areashaving a surface with a particular characteristic, (6) a geomagneticfield, (7) a correction to a geomagnetic field due to magneticstructures at or near the site, (8) a location of a reference position,or (9) a warning distance associated with a containment boundary.

In a 25th aspect, a navigation method for a wheeled object, thenavigation method comprising: obtaining an initial position of the wheelobject from a transmitter at a fixed, known position; obtaining aheading of the wheeled object from a magnetometer; obtaining a speed ofthe wheeled object through data from a wheel rotation counter, whereinthe wheel rotation counter comprises a tuning fork and a striker; andestimating a current position of the wheeled object based at least inpart on the initial position, the heading, and the speed.

In a 26th aspect, the method of aspect 25, further comprising: obtaininga heading of a castered wheel from a magnetometer; detecting casterchatter based, at least in part, on a comparison of the heading of thewheeled object and a heading of the castered wheel.

In a 27th aspect, the method of aspect 26, further comprising: omittingthe current position step when speed data is associated with casterchatter.

In a 28th aspect, a navigation method for a wheeled object, thenavigation method comprising: obtaining an initial position of the wheelobject from a transmitter at a fixed, known position; obtaining aheading of the wheeled object from a magnetometer; obtaining a speed ofthe wheeled object through data from a vibration sensor; and estimatinga current position of the wheeled object based at least in part on theinitial position, the heading, and the speed.

In a 29th aspect, the navigation method of aspect 28, furthercomprising: measuring a temperature of the magnetometer using atemperature sensor; and compensating for a temperature effect on themagnetometer.

In a 30th aspect, the navigation method of aspect 29, whereincompensating for the temperature effect on the magnetometer comprises:measuring the magnetometer output at three or more temperature pointsafter a printed circuit board assembly which contains the magnetometeris assembled; creating a calibration database containing the measurementdata; and computing a temperature compensation factor based at least inpart on polynomial interpolation of the calibration data based on themeasured temperature.

In a 31st aspect, the navigation method of any of aspects 28 to 30,further comprising: compensating for an alignment change between a truemagnetic field and a known geomagnetic field at the magnetometer.

In a 32nd aspect, the navigation method of aspect 31, wherein: aninitial alignment between the true magnetic field and the knowngeomagnetic field at the magnetometer is obtained through spinning thewheeled object around a vertical axis at an outdoor location away fromany large ferromagnetic objects; and a current alignment between thetrue magnetic and temperature field and the known geomagnetic field atthe magnetometer is obtained through a sufficient number of adequatelyspread heading readings over a sufficiently short period of time; andcompensating for the alignment change comprises: comparing the currentalignment with the initial alignment; replacing, if the initialalignment and the current alignment are significantly different, theinitial alignment with the current alignment; and computing the headingof the wheeled object based, at least in part, on the initial alignmentor the current alignment.

In a 33rd aspect, the navigation method of aspect 32, wherein asufficient number of adequately spread heading readings comprises: atleast 10% to 15% of the readings are in each quadrant of four magneticquadrants in the horizontal plane, and at least 25% of the readings arein two of the four magnetic quadrants.

In a 34th aspect, the navigation method of aspect 32 or aspect 33,wherein a sufficiently short period of time is 10 to 20 seconds.

In a 35th aspect, a system for detecting unauthorized shopping cartexits from a store, the system comprising: a dead reckoning systemattached to a shopping cart, the dead reckoning system having access toa store layout in a site configuration file, the store layout includingpositions of an exit and a checkout station; a locking wheel attached tothe shopping cart; wherein the dead reckoning system is configured to:estimate a position of the shopping cart at a plurality of time usingdead reckoning; detecting an exit event of the shopping cart; determine,based at least in part on the position estimate, whether the shoppingcart has passed through the checkout station before the exit event; andcommunicate, upon a determination that the shopping cart has not passedthrough the checkout station before the exit event, a locking command tothe locking wheel; and wherein the locking wheel is configured to engagea locking mechanism upon receiving the locking command from the deadreckoning system.

In a 36th aspect, the system of aspect 35, wherein the store layoutfurther includes a position of high-value merchandise area, and the deadreckoning system is configured to communicate the locking command upon adetermination that the shopping cart has passed through the high-valuemerchandise area without passing through the checkout station before theexit event.

In a 37th aspect, the system of aspect 35 or aspect 36, wherein the deadreckoning system is further configured to communicate the lockingcommand upon a determination that the shopping cart has passed throughthe checkout station without stopping before the exit event.

In a 38th aspect, the system of any of aspects 35 to 37, wherein thedead reckoning system is configured to estimate a speed of the shoppingcart based at least in part on an analysis of vibration or verticalacceleration data of the shopping cart.

In a 39th aspect, the system of any of aspects 35 to 38, wherein thestore layout further includes a magnetic field correction vector, andwherein the dead reckoning system is configured to correct a headingestimate using the magnetic field correction vector.

In a 40th aspect, the system of any of aspects 35 to 39, wherein thestore layout further includes a magnetic field correction vector map,and wherein the dead reckoning system is configured to correct a headingestimate using the magnetic field correction vector map and a currentposition of the shopping cart.

In a 41st aspect, the system of any of aspects 35 to 40, wherein thedead reckoning system is configured to trigger an audio alarm inconjunction with sending a locking command to the locking wheel.

In a 42nd aspect, the system of any of aspects 35 to 41, wherein thestore layout further includes a magnetic field map including locationsin the store and magnetic signatures at the locations, and wherein thedead reckoning system is configured to set its position to a location inthe magnetic field map upon detecting a magnetic signature correspondingto the location.

In a 43rd aspect, a navigation system for a human-propelled cart isprovided. The navigation system comprises a magnetometer configured todetermine a heading of the human-propelled cart; a vibration sensorconfigured to measure vibration data of the human-propelled cart; acommunication system configured to communicate with a wheel of thehuman-propelled cart, the wheel comprising a brake configured to inhibitrotation of the wheel in response to receipt of a locking signal; and ahardware processor programmed to: estimate a speed of thehuman-propelled cart based at least in part on the vibration data fromthe vibration sensor; and estimate a position of the human-propelledcart based at least in part on the estimated speed and the heading ofthe human-propelled cart.

In a 44th aspect, the navigation system of aspect 43, wherein toestimate the speed of the human-propelled cart based at least in part onvibration data from the vibration sensor, the hardware processor isprogrammed to analyze a spectrum of the vibration data.

In a 45th aspect, the navigation system of aspect 44, wherein to analyzethe spectrum of the vibration data, the hardware processor is programmedto identify a first peak in the spectrum of the vibration data, thefirst peak associated with vibration data for vibrations associated withforward or rearward movement of the human-propelled cart.

In a 46th aspect, the navigation system of aspect 45, wherein toestimate the speed of the human-propelled cart, the hardware processoris programmed to: determine a rotation rate of the wheel to be aharmonic frequency of the frequency of the first peak in the spectrum ofthe vibration data; and estimate the speed based on the rotation rateand a circumference of the wheel.

In a 47th aspect, the navigation system of aspect 46, wherein thehardware processor is programmed to validate the determined rotationrate by analyzing the vibration spectrum for presence of a second peakat a harmonic frequency of the first peak.

In a 48th aspect, the navigation system of aspect 47, wherein thehardware processor is programmed to analyze the spectrum for presence ofthe second peak at a first odd harmonic frequency of the first peak.

In a 49th aspect, the navigation system of any one of aspects 43 to 48,wherein the hardware processor is programmed to analyze the vibrationdata to count regular boundaries on a surface over which thehuman-propelled cart travels.

In a 50th aspect, the navigation system of any one of aspects 43 to 49,wherein the hardware processor is programmed to determine, based atleast in part on the estimated position, whether the cart has crossed acontainment boundary, and in response to the determination, tocommunicate the locking signal to the wheel.

In a 51st aspect, the navigation system of any one of aspects 43 to 50,further comprising a detector configured to detect an entrance signal oran exit signal indicative of whether the human-propelled cart isentering or exiting a store, respectively.

In a 52nd aspect, the navigation system of any one of aspects 43 to 51,further comprising a received signal strength indicator (RSSI) detector,wherein the hardware processor is programmed to update the estimatedposition of the cart based at least partly on a measured RSSI signal.

In a 53rd aspect, the navigation system of any one of aspects 43 to 52,further comprising a radio frequency (RF) receiver configured to receivean RF signal from an external RF transmitter, wherein the hardwareprocessor is programmed to update the estimated position of the cartbased at least partly on the received RF signal.

In a 54th aspect, the navigation system of aspect 53, wherein thehardware processor is programmed to estimate a distance to the externalRF transmitter based at least partly on an RF phase difference estimatedusing the RF signal.

In a 55th aspect, the navigation system of any one of aspects 43 to 54,further comprising a temperature sensor configured to measure atemperature of the magnetometer, wherein the hardware processor isprogrammed to compensate for temperature sensitivity of the magnetometerbased at least partly on temperature.

In a 56th aspect, the navigation system of any one of aspects 43 to 55,wherein the magnetometer is configured to provide a plurality ofmagnetic readings, and the hardware processor is programmed to calibratethe magnetometer based at least partly on the plurality of magneticreadings and a hard or soft iron calibration model.

In a 57th aspect, the navigation system of any one of aspects 43 to 56,wherein the hardware processor is further programmed to receive siteconfiguration data comprising information associated with one or moreof: (1) a containment boundary, (2) an entrance or an exit, (3) anindoor area of the site, (4) an outdoor area of the site, (5) areashaving a surface with a particular characteristic, (6) a geomagneticfield, (7) a correction to a geomagnetic field due to magneticstructures at or near the site, (8) a location of a reference position,or (9) a warning distance associated with a containment boundary.

In a 58th aspect, the navigation system of any one of aspects 43 to 57,wherein the vibration sensor comprises an accelerometer.

In a 59th aspect, the navigation system of any one of aspects 43 to 58,wherein the human-propelled cart comprises a handle, and the navigationsystem is mounted to the handle.

In a 60th aspect, the navigation system of aspect 59, wherein thehuman-propelled cart comprises a shopping cart. In another aspect, ashopping cart comprising the navigation system of any one of aspects 43to 60.

In a 61st aspect, a navigation method for a human-propelled wheeled cartis provided. The method comprises measuring, with a magnetometer, amagnetic heading of the human-propelled cart; measuring a spectrum ofvibrations experienced by the human-propelled cart as it travels over asurface; analyzing the spectrum of vibrations to determine a rotationrate of a wheel of the human-propelled cart; estimating a speed of thehuman-propelled cart based at least partly on the rotation rate of thewheel and a circumference of the wheel; and estimating a position of thehuman-propelled cart based at least partly on the estimated speed andthe measured magnetic heading of the human-propelled cart.

In a 62nd aspect, the navigation method of aspect 61, wherein analyzingthe spectrum of vibrations comprises identifying a first peak in thespectrum of vibrations associated with forward or rearward movement ofthe human-propelled cart.

In a 63rd aspect, the navigation method of aspect 62, wherein therotation rate of the wheel is determined to be a harmonic frequency ofthe frequency of the first peak in the spectrum of the vibration data.

In a 64th aspect, the navigation method of aspect 62 or aspect 63,further comprising validating the determined rotation rate by analyzingthe spectrum of vibrations for presence of a second peak at a harmonicfrequency of the first peak.

In a 65th aspect, the navigation method of any one of aspects 61 to 64,wherein analyzing the spectrum of vibrations comprises counting regularboundaries on the surface over which the human-propelled cart travels.

In a 66th aspect, the navigation method of any one of aspects 61 to 65,wherein the wheel comprises a brake configured to inhibit rotation ofthe wheel, the method further comprising: determining, based at least inpart on the estimated position, whether the human-propelled cart hascrossed a containment boundary; and in response to determining the carthas crossed the containment boundary, communicating a braking signal toactuate the brake in the wheel.

In a 67th aspect, the navigation method of any one of aspects 61 to 66,further comprising: measuring a temperature of the magnetometer; andcompensating for temperature sensitivity of the magnetometer based atleast partly on the measured temperature.

In a 68th aspect, the navigation method of any one of aspects 61 to 67,further comprising: measuring, with the magnetometer, a plurality ofmagnetic readings while the human-propelled cart is traveling over thesurface; and calibrating the magnetometer based at least partly on theplurality of magnetic readings and a hard or soft iron calibrationmodel.

In a 69th aspect, a human-propelled wheeled cart comprising a navigationsystem configured to perform the navigation method of any one of aspects61 to 68.

In a 70th aspect, the human-propelled wheeled cart of aspects 69,wherein the navigation system is mounted on or included in a handle ofthe cart.

In a 71st aspect, the human-propelled wheeled cart of aspect 69 oraspect 70, wherein the cart comprises a shopping cart.

In a 72nd aspect, an anti-theft system for a human-propelled cart, theanti-theft system comprising: a vibration sensor configured to measurevibration data of the human-propelled cart; a communication systemconfigured to communicate with a wheel of the human-propelled cart, thewheel comprising a brake system configured to inhibit rotation of thewheel in response to receipt of a locking signal; and a hardwareprocessor programmed to: analyze the vibration data to determine thecart has received an impulse; analyze the vibration data to determine avibration signature indicative of ringing of the cart in response to theimpulse; estimate, based at least partly on the analysis of thevibration data, whether the cart is loaded or unloaded; determinewhether the cart has crossed a confinement boundary; determine, based atleast partly on the estimate of whether the cart is loaded or unloadedand whether the cart has crossed the confinement boundary, an anti-theftinstruction to communicate to the brake system or to an externalsurveillance system; and communicate the instruction.

In a 73rd aspect, the anti-theft system of aspect 72, wherein thevibration sensor comprises an accelerometer.

In a 74th aspect, anti-theft system of aspect 72 or aspect 73, whereinto analyze the vibration data to determine the cart has received animpulse, the hardware processor is programmed to identify a verticalcomponent of acceleration with magnitude exceeding 0.5 g and having aduration less than 10 ms.

In a 75th aspect, the anti-theft system of any one of aspects 72-74,wherein to analyze the vibration data to determine a vibration signatureindicative of ringing of the cart in response to the impulse, thehardware processor is programmed to identify a horizontal component ofacceleration having a frequency greater than 1 kHz that occurs within 10ms of the impulse, the horizontal component in a direction of cartmotion.

In a 76th aspect, the anti-theft system of any one of aspects 72-75,wherein to determine an estimate of whether the cart is loaded orunloaded, the hardware processor is programmed to determine whether avibration signal in a direction of cart motion is above or below athreshold vibration amplitude.

In a 77th aspect, the anti-theft system of any one of aspects 72-76,wherein the anti-theft instruction comprises an instruction to actuatethe brake system if the cart is estimated to be loaded.

In a 78th aspect, the anti-theft system of any one of aspects 72-77,wherein the anti-theft instruction comprises an instruction to actuatethe brake system, wherein the instruction further comprises anindication of a speed or force at which the brake system is to beapplied to slow the cart, and wherein the indication of the speed orforce depends at least partly on the estimate of whether the cart isloaded or unloaded.

In a 79th aspect, the anti-theft system of any one of aspects 72-78,wherein the anti-theft instruction comprises an instruction to notactuate the brake system if the cart is estimated to be unloaded.

In an 80th aspect, the anti-theft system of any one of aspects 72-79,wherein the anti-theft instruction comprises an instruction to actuatethe external surveillance system if the cart is estimated to be loaded.

In an 81st aspect, the anti-theft system of any one of aspects 72-80,further comprising a navigation system configured to determine alocation of the cart.

In an 82nd aspect, the anti-theft system of aspect 81, wherein thenavigation system comprises: a magnetometer configured to determine aheading of the cart, wherein the hardware processor is furtherprogrammed to: estimate a speed of the cart based at least in part onthe vibration data from the vibration sensor; and estimate a location ofthe cart based at least in part on the estimated speed and the headingof the cart.

In an 83rd aspect, the anti-theft system of aspect 82, wherein toestimate the speed of the cart, the hardware processor is programmed to:analyze a spectrum of the vibration data; identify a first peak in thespectrum of the vibration data, the first peak associated with vibrationdata for vibrations associated with forward or rearward movement of thecart; determine a rotation rate of the wheel to be a harmonic frequencyof the frequency of the first peak in the spectrum of the vibrationdata; and estimate the speed based on the rotation rate and acircumference of the wheel.

In an 84th aspect, a method for determining whether a human-propelledwheeled cart is loaded or unloaded, the method comprising: measuring,with a vibration sensor, a Z-vibration signature representative of animpulse to the cart in a vertical, Z-direction; measuring, with thevibration sensor, an X-vibration signature representative of ringing ofthe cart in response to the impulse, the X-vibration signature in ahorizontal, X-direction parallel to a direction of motion of the cart;and determining whether the cart is loaded or unloaded based at leastpartly on the X-vibration signature.

In an 85th aspect, the method of aspect 84, wherein the Z-vibrationsignature comprises an acceleration in the Z-direction having amagnitude greater than 1 g and a duration of less than 10 ms.

In an 86th aspect, the method of aspect 84 or aspect 85, wherein theX-vibration signature has a frequency greater than 1 kHz and occurswithin 10 ms of the impulse.

In an 87th aspect, the method of any one of aspects 84-86, whereinestimating the weight of the cart comprises comparing an amplitude ofacceleration associated with the X-vibration signature to a threshold.

In an 88th aspect, the method of aspect 87, wherein the threshold is 1g.

In an 89th aspect, the method of any one of aspects 84-88, furthercomprising estimating a weight of the cart or a weight of the cart loadbased at least partly on the X-vibration signature. In aspect 89-A, themethod of any one of aspects 84-89, further comprising: in response todetermining that the cart is loaded, actuating a brake system configuredto inhibit motion of the cart. An aspect 89-B, the method of aspect89-A, further comprising providing an indication of a speed or force atwhich the brake system is to be applied to slow the cart, wherein theindication of the speed or force depends at least partly on thedetermination that is loaded. In aspect 89-C, the method of any one ofaspects 84-89, 89-A, or 89-B, further comprising: estimating a speed ofthe cart based at least in part on vibration data from a vibrationsensor; and estimating a location of the cart based at least in part onthe estimated speed and a heading of the cart.

In a 90th aspect, a navigation system for a human-propelled, wheeledcart, the navigation system comprising: a light detector configured todetect ambient light data along a path traveled by the cart;non-transitory memory configured to store lighting signature datarepresentative of a cart environment; and a hardware processor incommunication with the light detector and the non-transitory memory, thehardware processor programmed to: analyze the ambient light data and thelighting signature data to determine a location of the cart in the cartenvironment.

In a 91st aspect, the navigation system of aspect 90, wherein the lightdetector comprises a photosensor.

In a 92nd aspect, the navigation system of aspect 90 or aspect 91,wherein the lighting signature data comprises, for an ambient lightsource, one or more of: a horizontal position of the light source, aheight of the light source, an optical power of the light source, or anangular dependence of optical power of the light source.

In a 93rd aspect, the navigation system of any one of aspects 90-92,wherein to analyze the ambient light data and the lighting signaturedata to determine a location of the cart in the cart environment, thehardware processor is programmed to reduce or minimize an error functionbased at least partly on a previous cart location, the ambient lightdata, and the lighting signature data.

In a 94th aspect, the navigation system of any one of aspects 90-93,wherein the hardware processor is further programmed to check a timehistory of the ambient light data to determine whether the time historyis consistent with the measured velocity or direction of motion of thecart.

In a 95th aspect, the navigation system of any one of aspects 90-94,further comprising: a dead reckoning system configured to estimate cartlocation based at least partly on measurement of wheel rotation and cartheading.

In a 96th aspect, the navigation system of aspect 95, wherein to analyzethe ambient light data and the lighting signature data to determine alocation of the cart in the cart environment, the hardware processor isfurther programmed to utilize the cart location estimated by the deadreckoning system.

In a 97th aspect, a human-propelled, wheeled cart comprising: a firstmagnetometer configured to record first magnetic data, the firstmagnetometer disposed at a first height; a second magnetometerconfigured to record second magnetic data, the second magnetometerdisposed at a second height that is different from the first height; anda navigation system configured to receive the first magnetic data andthe second magnetic data, the navigation system further configured todetermine a location of the cart based at least partly on the firstmagnetic data, the second magnetic data, or both the first and thesecond magnetic data.

In a 98th aspect, the human-propelled, wheeled cart of aspect 97,wherein: the first magnetometer is mounted to a handle of the cart; andthe second magnetometer is mounted to a rail of a basket of the cart,the rail disposed below the handle of the cart.

In a 99th aspect, the human-propelled, wheeled cart of aspect 97 oraspect 98, wherein: the first magnetometer is disposed in the navigationsystem which is mounted to a handle of the cart; and the secondmagnetometer is disposed in a wheel of the cart.

In a 100th aspect, the human-propelled, wheeled cart of any one ofaspects 97-99, wherein: the navigation system is configured to determinea first location of the cart based at least partly on the first magneticdata, the first location associated with a first confidence; thenavigation system is configured to determine a second location of thecart based at least partly on the second magnetic data, the secondlocation associated with a second confidence; and the navigation systemis configured to determine the location of the cart based at leastpartly on the first location, the second location, the first confidence,and the second confidence.

In 101st aspect, the human-propelled, wheeled cart of any one of aspects97-100, wherein the navigation system is configured to store a magneticfield map of an environment for the cart, the magnetic field mapcomprising a multi-layer map having first magnetic signaturescorresponding to the first height and second magnetic signaturescorresponding to the second height.

In a 102nd aspect, the human-propelled, wheeled cart of aspect 101,wherein the navigation system is configured to determine the location ofthe cart based at least partly on the magnetic field map.

In a 103rd aspect, a positioning system for a human-propelled cart, thenavigation system comprising: a vertical position detector;non-transitory memory configured to store a multi-level map containinginformation on a plurality of levels within an environment in which thecart can move; and a navigation system in communication with thevertical position detector and the non-transitory memory, the navigationsystem configured to determine a location of the cart within theenvironment based at least partly on a measurement from the verticalposition detector and information in the multi-level map, the locationof the cart comprising a horizontal location within the environment andan identification of one of the plurality of levels on which the cart islocated.

In a 104th aspect, the positioning system of aspect 103, wherein thevertical position detector comprises a pressure sensor, an altimeter, oran accelerometer.

In a 105th aspect, the positioning system of aspect 103 or aspect 104,wherein the navigation system comprises a dead reckoning system.

In a 106th aspect, the positioning system of any one of aspects 103-105,wherein the vertical position detector comprises a pressure sensor, andthe navigation system is configured to: receive a reference pressuremeasured by a reference pressure sensor located within the environment;and determine an altitude of the cart relative to an altitude of thereference pressure sensor.

In a 107th aspect, the positioning system of any one of aspects 103-106,wherein the vertical position detector comprises an accelerometer, andthe navigation system is configured to integrate acceleration data fromthe accelerometer to determine a vertical displacement of the cart.

In a 108th aspect, the positioning system of any one of aspects 103-107,further comprising: a vibration sensor; and a wheel rotation detector;wherein the navigation system is configured to use vibration data fromthe vibration sensor, absence of measured wheel rotation, and a locationestimate that the cart is near an entrance to a cart conveyor system todetermine the location of the cart.

Additional Information

The various illustrative logical blocks, modules, and processesdescribed herein may be implemented or performed by a machine, such as acomputer, a processor, a digital signal processor (DSP), an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) or other programmable logic device, discrete gate or transistorlogic, discrete hardware components, or any combination thereof designedto perform the functions described herein. A processor may be amicroprocessor, a controller, microcontroller, state machine,combinations of the same, or the like. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors orprocessor cores, one or more graphics or stream processors, one or moremicroprocessors in conjunction with a DSP, or any other suchconfiguration.

Further, certain implementations of the object location systems of thepresent disclosure are sufficiently mathematically, computationally, ortechnically complex that application-specific hardware (e.g., FPGAs orASICs) or one or more physical computing devices (utilizing appropriateexecutable instructions) may be necessary to perform the functionality,for example, due to the volume or complexity of the calculationsinvolved (e.g., analyzing the vibration data and performing the deadreckoning navigation calculations) or to provide results (e.g.,statistical information on the object locations) substantially inreal-time.

The blocks or states of the processes described herein may be embodieddirectly in hardware, in a software module stored in a non-transitorymemory and executed by a hardware processor, or in a combination of thetwo. For example, each of the processes described above may also beembodied in, and fully automated by, software modules (stored in anon-transitory memory) executed by one or more machines such ascomputers or computer processors. A module may reside in anon-transitory computer readable medium such as RAM, flash memory, ROM,EPROM, EEPROM, registers, hard disk, an optical disc, memory capable ofstoring firmware, or any other form of computer-readable (e.g., storage)medium. A computer-readable medium can be coupled to a processor suchthat the processor can read information from, and write information to,the computer-readable medium. In the alternative, the computer-readablemedium may be integral to the processor. The processor and thecomputer-readable medium may reside in an ASIC. The computer-readablemedium may include non-transitory data storage (e.g., a hard disk,non-volatile memory, etc.).

The processes, methods, and systems may be implemented in a network (ordistributed) computing environment. For example, the central controlunit or base station may be implemented in a distributed, networked,computing environment. Network environments include enterprise-widecomputer networks, intranets, local area networks (LAN), wide areanetworks (WAN), personal area networks (PAN), cloud computing networks,crowd-sourced computing networks, the Internet, and the World Wide Web.The network may be a wired or a wireless network, a terrestrial orsatellite network, or any other type of communication network.

Depending on the embodiment, certain acts, events, or functions of anyof the processes or methods described herein can be performed in adifferent sequence, may be added, merged, or left out altogether. Thus,in certain embodiments, not all described acts or events are necessaryfor the practice of the processes. Moreover, in certain embodiments,acts or events may be performed concurrently, e.g., throughmulti-threaded processing, interrupt processing, or via multipleprocessors or processor cores, rather than sequentially. In anyapparatus, system, or method, no element or act is necessary orindispensable to all embodiments, and the disclosed apparatus, systems,and methods can be arranged differently than shown or described.

Conditional language used herein, such as, among others, “can,” “could,”“might,” “may,” “e.g.,” and the like, unless specifically statedotherwise, or otherwise understood within the context as used, isgenerally intended to convey that certain embodiments include, whileother embodiments do not include, certain features, elements and/orstates. Thus, such conditional language is not generally intended toimply that features, elements and/or states are in any way required forone or more embodiments or that one or more embodiments necessarilyinclude logic for deciding, with or without author input or prompting,whether these features, elements and/or states are included or are to beperformed in any particular embodiment. The terms “comprising,”“including,” “having,” and the like are synonymous and are usedinclusively, in an open-ended fashion, and do not exclude additionalelements, features, acts, operations, and so forth. Also, the term “or”is used in its inclusive sense (and not in its exclusive sense) so thatwhen used, for example, to connect a list of elements, the term “or”means one, some, or all of the elements in the list.

Conjunctive language such as the phrase “at least one of X, Y and Z,”unless specifically stated otherwise, is otherwise understood with thecontext as used in general to convey that an item, term, etc. may beeither X, Y or Z. Thus, such conjunctive language is not generallyintended to imply that certain embodiments require at least one of X, atleast one of Y and at least one of Z to each be present. The articles“a” or “an” or “the” when referring to an element means one or more ofthe element, unless the context clearly indicates otherwise.

While the above detailed description has shown, described, and pointedout novel features as applied to various embodiments, it will beunderstood that various omissions, substitutions, and changes in theform and details of the logical blocks, modules, and processesillustrated may be made without departing from the spirit of thedisclosure. As will be recognized, certain embodiments of the inventionsdescribed herein may be embodied within a form that does not provide allof the features and benefits set forth herein, as some features may beused or practiced separately from others.

What is claimed is:
 1. A human-propelled, wheeled cart comprising: afirst magnetometer configured to record first magnetic data, the firstmagnetometer disposed at a first height; a second magnetometerconfigured to record second magnetic data, the second magnetometerdisposed at a second height that is different from the first height; anda navigation system configured to receive the first magnetic data andthe second magnetic data; the navigation system further configured todetermine: a first location of the cart based at least partly on thefirst magnetic data, the first location associated with a firstconfidence; a second location of the cart based at least partly on thesecond magnetic data, the second location associated with a secondconfidence; and a location of the cart based at least partly on (i) thefirst location and the second location and (ii) the first magnetic data,the second magnetic data, or both the first and the second magneticdata.
 2. The human-propelled, wheeled cart of claim 1, wherein the firstand second magnetometers are fixed to a frame of the cart.
 3. Thehuman-propelled, wheeled cart of claim 1, wherein: the firstmagnetometer is mounted to a handle of the cart; and the secondmagnetometer is mounted to a rail of a basket of the cart, the raildisposed below the handle of the cart.
 4. The human-propelled, wheeledcart of claim 1, wherein the first or the second magnetometer is coupledto a frame of the cart.
 5. The human-propelled, wheeled cart of claim 1,wherein the navigation system is further configured to determine thelocation of the cart based at least partly on the first confidence andthe second confidence.
 6. The human-propelled, wheeled cart of claim 5,wherein the location of the cart comprises a weighted average of thefirst location and the second location, and wherein weights of theweighted average are based at least partly on the first and the secondconfidences.
 7. The human-propelled, wheeled cart of claim 1, whereinthe navigation system is configured to: determine that the firstlocation does not match the second location; and in response to thedetermination that the first location does not match the secondlocation: determine the location of the cart as being between the firstlocation and the second location; or determine the location using abacktrack algorithm.
 8. The human-propelled, wheeled cart of claim 1,wherein the navigation system is further configured to: store a magneticfield map of an environment for the cart, the magnetic field mapcomprising a multi-layer map having first magnetic signaturescorresponding to the first height and second magnetic signaturescorresponding to the second height; and determine the location of thecart based at least partly on the magnetic field map.
 9. Ahuman-propelled, wheeled cart comprising: a first magnetometerconfigured to record first magnetic data, the first magnetometerdisposed at a first height; a second magnetometer configured to recordsecond magnetic data, the second magnetometer disposed at a secondheight that is different from the first height; and a navigation systemconfigured to receive the first magnetic data and the second magneticdata, the navigation system further configured to: store a magneticfield map of an environment for the cart, the magnetic field mapcomprising a multi-layer map having first magnetic signaturescorresponding to the first height and second magnetic signaturescorresponding to the second height; determine a location of the cartbased at least partly on (i) the magnetic field map and (ii) the firstmagnetic data, the second magnetic data, or both the first and thesecond magnetic data.
 10. The human-propelled, wheeled cart of claim 9,wherein the first and second magnetometers are fixed to the frame. 11.The human-propelled, wheeled cart of claim 9, wherein: the firstmagnetometer is disposed in the navigation system which is mounted to ahandle of the cart; and the second magnetometer is disposed in a wheelof the cart.
 12. The human-propelled, wheeled cart of claim 9, whereinthe first or the second magnetometer is coupled to a basket of the cart.13. The human-propelled, wheeled cart of claim 9, wherein the navigationsystem is further configured to determine: a first location of the cartbased at least partly on the first magnetic data, the first locationassociated with a first confidence; a second location of the cart basedat least partly on the second magnetic data, the second locationassociated with a second confidence; and the location of the cart basedat least partly on the first location and the second location.
 14. Thehuman-propelled, wheeled cart of claim 9, wherein the navigation systemis further configured to determine the location of the cart based atleast partly on detecting a match between the first magnetic data andthe first magnetic signatures or a match between the second magneticdata and the second magnetic signatures.
 15. The human-propelled,wheeled cart of claim 9, wherein the navigation system is furtherconfigured to communicate the magnetic field map and cart navigationhistory data to a remote processor.
 16. The human-propelled, wheeledcart of claim 15, wherein the remote processor is programmed to analyzethe magnetic field map and the cart navigation history data to determinechanges in the magnetic field map.
 17. The human-propelled, wheeled cartof claim 15, wherein the remote processor is further programmed to learna magnetic signature of a structure in which the cart is propelled basedat least partly on the determined changes in the magnetic field map. 18.The human-propelled, wheeled cart of claim 9, wherein the navigationsystem is further configured to determine a correction vector tocompensate for distortions in a geomagnetic field at the location of thecart.
 19. The human-propelled, wheeled cart of claim 18, wherein thecorrection vector is determined to at least partially compensate forhorizontally or vertically stratified magnetic anomalies in a structurein which the cart is propelled.